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Monroe Calculating Machines

Introduction
My Model F
   Video
My Model K
   Video
My Model KA
My Model L
   Video
How to use the Monroe
History
Paraphernalia
Books, Manuals
Advertisements and Articles
Patents
Links

The Monroe Calculating Machine Company was founded in 1912. Their first calculators had a hand crank and a moving carriage, similar to the Odhner pinwheel calculators, but for entering numbers it had a keyboard similar to a Comptometer instead of dials or sliders. This allowed anyone familiar with the pinwheel calculators to use it with little practise and to perform calculations much faster than before. Although the Comptometer was still faster in operation, it needed a lot of training to reach that speed on a Comptometer compared to the Monroe. Monroe machines really became popular once they became electrically driven.

Model F

This Monroe model F has the serial number F6533. The serial number can be found on the back plate of the machine, just above the Monroe decal. This model was made in 1917 and 1918. The later model K (see below) inherited many features of this machine, but often in an improved or simplified form.

The case of the machine is rectangular, with sharp edges and corners, made of metal sheets screwed onto a frame and painted black. It has a full keyboard with 8 columns of keys. The crank is on the right hand side. The carriage is at the back, and has a more rounded shape than the case. It has a register with 16 digits, and an 8-digit counter. The counter does not have a carry mechanism, and uses red digits for negative numbers as used in division. The small handle on the right of the carriage is turned clockwise to clear the counter, and anti-clockwise to clear the register. Note that you have to lift the carriage when clearing the register in order to disengage it from the main mechanism.

The rod that the carriage slides on is easily unscrewed and removed, after which the carriage comes off. You can then see the stepped drums that drive the register. The drums are split, with one part having 5 teeth and the other 0 to 4 teeth, so together any number from 0 to 9 can be made. Pressing a key shifts the two halves of the stepped drum into the plane of the intermediate gear that turns the register's number wheel. Note that these stepped drums are simply discs with pins of various lengths sticking out from the side.

There are a number of complications in the mechanism of the model F that have been simplified in the model K. When the crank of the model F is given a full turn, the mechanism goes through two separate stages. With addition the crank is given a clockwise turn, and the first stage starts at the top marking and continues until the crank reaches the bottom marking. During this first half of the cycle the stepped drums are rotated a full turn, adding the input to the register. If any digit rolls over from 9 to 0, a switch is tripped to store that fact. The second half of the cycle, when the crank moves from the bottom marking to the top one, is when the carry is performed. The carry drum rotates throughout the cycle, doing one full turn. This drum has a series of pins, arranged as a helix on one side of the drum. Any previously tripped carry switch causes a pin to slide to the left, which in turn catches a tooth of the next intermediate wheel, incrementing the next digit.

Subtraction uses the same process as addition, except that the crank turns in the opposite direction, as do the stepped drums and the carry drum. The first half is when the crank moves from the bottom marking to the top marking, and again this is when the input is transferred to the register, but subtracted this time, and any digits that roll over trip a carry switch. The carry is performed in the second half, when the crank moves from the top marking to the bottom one. The carry still needs to be performed from right to left, so now the helical arrangement of pins on the carry drum needs to spiral in the opposite direction. This is a problem, because the same half of the carry drum already has the addition helix and this interferes. To remedy this problem part of each helix has been made movable so that it is used in both operations.

Video

This video demonsatrates my Monroe Model F calculator.

This video takes a closer look at the mechanism of the Monroe Model F calculator.

Model K

This Monroe model K has the serial number K160-144100. The serial number can be found on the front of the machine, at the bottom edge. The 3-digit number specifies the exact variant of the model, where the first two of those digits show the length of the register, and the third is the series number. I do not know the difference between the various series, except that the series 3 has two counter registers.

There are glass windows on the carriage in front of the register and counter. This seems to be an optional extra, as not all machines have this.

The crank is on the right hand side. There is a small metal lever next to the keyboard that releases a catch, allowing the crank to be removed.

The standard keyboard has 8 columns of keys, but there are also versions with just 6 columns and a narrower body, and versions with 10 columns and a wider body. Many 8-column model K's were given the same wider case that the 10-column version used. As the carry mechanism for the register is housed in the body of the machine, no carries are performed on the register digits that extend past the left side of the body. The wider body on such model K machines allows a few extra digits to have carry.

The carriage is easily detached - just remove one screw and the rod it slides on can be removed. You can then see the stepped drums that drive the register. The drums are split, with one part having 5 teeth and the other 0 to 4 teeth, so together any number from 0 to 9 can be made. Pressing a key shifts the two halves of the stepped drum into the plane of the register's connecting gear.

Many of the aspects of the model F and G mechanism have been improved and simplified in the model K. One big improvement is that the carriage automatically lifts when clearing the main register, though this functionality was already present in the latest versions of the model G. In the model F/G there is a comb above the keyboard which ensures the carriage is aligned. In the model K this has been combined with the carriage shift mechanism.

The crank cycle has also been greatly simplified. The stepped drums have changed so that their teeth span only half their circumference, so that they can turn continuously through the crank cycle but only engage for half the cycle. The helical arrangement of pins on the carry drum has changed so that each helix spans only about a quarter turn of the axle, and are in separate regions of the drum so do not interfere with each other any more. During addition the first quarter turn of the cycle does nothing except allow the carry pins for subtraction to move past the register, the next half turn adds the input to the register through the stepped drums, and in the final quarter turn the carry operations for addition are performed. The subtraction cycle is essentially the same.

Here is another model K, and this one has the serial number 119910. This number is not prefixed by the exact model, but it seems to be a K160. It does not have glass windows over the registers.

Video

This video gives a better look at the mechanism.

Model KA

This Monroe model KA has the serial number KA160-129883. It is an electrically driven version of the model K - the A stands for Automatic - and has a 16-digit register as indicated by the first two digits.

The calculator has some problems apart from the trivial cosmetic issues. The electrical wiring of this calculator has deteriorated badly, and needs to be replaced. The Clear button should have a large red key top but it has been replaced by a black key labelled Error. There are two small parts missing: There should be a mount at the top left of the keyboard that holds the linkage between the locking bar of the keyboard and the rotary mechanism (this prevents keys being pressed while the calculator is performing an operation). Also a ring is missing on the axle of the carriage shifting knob, which can cause the axle to shift forward and collide with the calculation mechanism. Overall, the mechanism seems to be in working order since it will add or subtract if you twist the knob on the right hand side where a hand crank would be on the manual version.

Model L

This is a Monroe model L, which has the serial number L-200X-228247. The model L is mechanically virtually identical to the model K, except that it is about half the size, and therefore much lighter. This one has a 20-digit register, as indicated by the first two digits in the model number. I do not know what the X indicates. This machine has 10 keyboard columns, but 8 is also common.

It is in very good condition, apart from some wear to the left side of the keyboard, and a curved scratch from the crank. The casing is beautifully painted in black crackle paint with a dark green undercoat. It does not have the Item Count knob that the model K has, and though there is a small hole where something could be fitted. Although the pictures in advertisements I found also never show anything there, there are pictures online of a model L with a clasp that can hold down the 1 button.

As with the model K, the carriage is easily detached, revealing the underlying mechanism. It works exactly the same way as its larger predecessors, with a split stepped drum.

The serial number is stamped on the inside of the inner frame, but can be seen through a slot in the bottom of the case.

Video

This video demonsatrates my model K and model L Monroe calculators.

How to use the Monroe

Adding, Subtracting: A Monroe machine typically has a keyboard that has 8 columns of keys. Each column has 10 keys, numbered from 0 to 9. When you press a key to select a digit, the key stays pushed in. If you push a second key in the same column, the first key pops back up so that you can only select (at most) one digit in a column. After entering a number in this way, you can turn the hand crank on the right of the machine. Turning the crank clockwise once adds the selected number to the register, and turning it the other way subtracts it. On an electrically driven model you have to press the Plus (+) button or the Minus (-) button to activate the motor instead of turning a crank.

(Non) Repeat: At the right of the keyboard are three buttons. The largest one is labelled Clear or 0, and it clears the selected number from the keyboard, causing all pushed-in buttons to pop up. The other two buttons are marked Repeat (or R), and Non-Repeat (or blank), and when one of them is pressed, the other pops up. When Non-Repeat is selected, the keyboard will be cleared automatically when the turn of the hand crank is completed. When Repeat is selected this does not happen, so that you can turn the crank repeatedly to add the selected number to the register several times, thereby performing a small multiplication.

Multiplication: The register, typically 16 digits long, is located in a carriage at the back of the machine, like a standard typewriter. The carriage can be moved along a digit to the left or right by turning a handle at the front of the machine. This allows you to add 10 times the selected number to the register with each turn of the hand crank, and by shifting the carriage again you can add 100 times the selected number, and so on. In this way it becomes easy to do large multiplications. For example, to multiply the number you entered by 123, you would make sure that Repeat was pressed down, and then turn the crank three times, shift the carriage to the right, turn the crank twice, shift the carriage again, and turn the crank once more.

Carry: It should be noted that the register does not have a carry mechanism inside the carriage. Carries are handled by rotary mechanism in the body of the machine that drives the register. This means that if the carriage is shifted to the left and sticks out, the digits of the register in that part of the carriage will not be updated by a turn of the hand crank, and only the digits aligned with the keyboard will update together with two or three further digits on the left. In practice this rarely becomes a problem, especially since a warning bell sounds when a carry occurs that cannot be handled.

The counter: The carriage also has a second smaller register which acts as a counter. Every time you turn the crank to add a number, the counter increments the digit that is lined up with the right column of the keyboard. If you subtract a number, the digit will be decremented. The digits shown can be the values 0 to 9 displayed in black, but when a digit gets decremented below zero, it will show as a red digit 1 to 9 to represent -1 to -9. In a multiplication, the counter keeps track of what number you have multiplied the selected number by so far, and similarly in a division it shows the number of times you have subtracted so far. Note however that the counter does not perform any carries, so if you turn the crank more than 9 times without moving the carriage, the counter's digit will roll over from +9 to -9 or vice versa without adjusting the next digit in the counter.

Clearing: A clockwise turn of the handle on the right of the carriage will clear the counter, and an anti-clockwise turn clears the register.

Item Count: If you need a counter that does perform carries, then you can use some columns in the main register. To this end there is often a knob to the left of the keyboard labelled Item Count. If you turn that knob clockwise, and press down the 1 key in the left column, that key will become locked down. It will not be cleared with the rest of the selected number. This gives you a 3-digit counter in columns 8 to 10 of the main register which will count the number of turns of the crank. When adding a long list of numbers, it gives you how many numbers were in the list.

History

The Monroe Calculating Machine Company was founded by Jay R. Monroe in 1912 in order to make calculators based on the latest design by Frank Baldwin. Baldwin had invented many different calculation machines, but was unable to market them successfully for many years. Monroe was able to turn Baldwin's design into a good working machine that could be sold to the public.

The first Monroe calculator was the model A in 1911/1912. Very little is known about the model A, as very few were made, and possibly none are even in existence now. Pictures of these older machines show that the drive gears connected to the crank are on the outside of the case, and that there are separate clearing handles for the counter and register. Larger scale production started with the model D in 1914. This was followed by the models E, F, and G over the next few years. These were increasingly successful, but are relatively rare today. The model K was released in 1921.

Note that it seems that these early model letters simply denote the year it was first made, from A in 1911 to K in 1921. It is unclear if there were any models designated B, C, H, I and J, but if so, they were probably prototypes. Model D was a big improvement over A, and similarly K was a big change over model G, so they took a few years to develop. Even so, the model G did receive small improvements during its production run. The exact start of the model G's production is unclear, as the advertisements do not mention the model letters, but the carriage lock rail of the model G can definitely be seen in ads from February 1919.

The model K was released in 1921, and produced through most of the 1920s. It was commercially very successful, even though functionally it is actually not very different to the previous models. What may have helped its success is that an electrically driven version was made, the model KA where the A stands for automatic. Frank Baldwin lived to see the beginnings of this success, as he died in 1926.

In 1929 Monroe made the model L which is virtually the same as the model K except that it is minituarised to about half the size. Whereas the model K is large and very heavy, and the model KA even more so with its heavy electric motor, the model L is much more portable. Versions of the model L/LA were produced until the 1960s. Several further calculator models followed, most of them electrically driven.

Here is a table listing the early calculator models. It seems that for each new model the serial numbers start from some round figure higher than those of the previous model. It is not known exactly how many were made of each model, so I have listed the highest number I have found in each case.

They also produced many listing calculating machines. This started when Monroe bought the Gardner Calculator Company in about 1929. Clyde Gardner had worked for the Pike Adding Machine Company, and for Burroughs after they bought Pike, but set up his own company in 1923 to produce the adding-listing machine that he designed. He died shortly after, but his company continued until it was bought by Monroe. At first the machines were branded Monroe-Gardner, but in 1936 the Gardner name was dropped. Monroe also made other office machines including check writing and signing equipment.

In 1958, the company was bought by Litton Industries, but continued to produce machines under the Monroe name. In the 1970s they transitioned to electronic calculators, but also had to diversify to producing other office machines such as accounting machines, copiers and shredders. In 1980 their name changed to Monroe Systems for Business to reflect that transition. The company still exists, and supplies their own business products as well as those by other manufacturers.

In the Monroe service training manual from 1957 there is a nice detailed history of the founding of the Monroe company, which I reproduce here:

OUR BEGINNING

FIGURING SERVICE AND EDUCATION ARE SIGNIFICANT FACTORS IN THE NOTABLE GROWTH OF MONROE, THE PIONEER CALCULATING MACHINE MANUFACTURER

Within the archives of the history of American Technical Progress lies something more than a mere record of the development of the marvelous mechanical and electronic devices which today, many years later, continue to keep the wheels of industry and business turning smoothly. This chapter from 1911 to date includes the story of the Monroe Calculating Machine and its valuable contribution to the advance of civilization through practical education, a broadening of opportunities and a widening of horizons. A prominent part in this modern industrial march has been taken by the Monroe Calculating Machine Company, which in 1957 celebrates its forty-fifth anniversary.

It was in 1911 that Jay. R. Monroe, President and Founder of the Monroe Company, first saw the Baldwin Calculator the invention of Frank Stephen Baldwin. This machine was the first reversible, crank type calculating machine. Although Mr. Baldwin’s machine had been patented in 1874 and had been judged by the Franklin Institute as the most noteworthy invention of that year, it had not been developed for commercial use.

Mr. Monroe recognized the merits of the Baldwin Calculator, and saw in this machine, which others had said was "ahead of its time," possibilities for the development of a figuring device which would be invaluable in the business world. He joined forces with Mr. Baldwin and, adopting the basic principles of the Baldwin machine, built a calculator which met Mr. Monroe's requirements. It was simple to operate, performing direct subtraction and division as easily as addition and multiplication, a device which could immediately handle all the figure work of any office without the services of a highly trained operator.

Mr. Monroe was at that time still in his twenties. During his brief business experience, however, he had taken advantage of the opportunity to study at first hand the figuring needs of the business office. After being graduated from a mid-western university, he associated with the Western Electric Company in Chicago, where his work necessitated a study of accounting methods. Later he moved to the Pittsburgh offices of that company. In 1910 he transferred to their New York offices and was still located there when he met Mr. Baldwin the following year.

In April 1912 he organized the Monroe Calculating Machine Company, and in a small rented room near Newark, New Jersey, the manufacture of the first Monroe Adding-Calculator was begun. When the new machine was exhibited for the first time at the National Business Show in New York that fall, it was viewed by business executives from all parts of the country and was described as one of the mechanical marvels of the day.

The following year the firm moved to Orange, New Jersey, and occupied part of the first and second floors of the building which now houses the Company executive offices. The factory personnel consisted of only nine men* and the entire heavy factory equipment was a lathe and two small presses. Even with these meager tools, tolerances were maintained to within thousandths of an inch to insure the accurate performance of the. finished machine. This was a noteworthy accomplishment at that time.

* Mr. Monroe's first two assistants are still alive. One, Mr. Sidney Smith recently retired, the other, Mr. John Bergman, is an active Orange Supervisor.

When the first Monroe was offered to the business world in 1914, it was immediately recognized by many progressive executives as a valuable instrument of economy. Yet it required ability, energy, and a firm belief in the machine to overcome the prejudices of many who were reluctant to change their time-honored methods of performing computations. However, by perseverance, sales were made and a market was developed.

The demand for the machine increased rapidly and expansion in manufacturing facilities became necessary. The original factory building was soon outgrown and the plant was enlarged to twice its capacity. Two years later, a modern, four- story concrete building fully equipped with up-to-date machinery again doubled the Company's manufacturing facilities. In the next few years purchases were made of additional properties until now the Company's plants occupy large areas in Orange and Morris Plains, New Jersey; Bristol, Virginia; and Amsterdam, Holland.

Early in the Company's history, sales representatives were carrying the story of Monroe figuring economies throughout the United States, and shortly to Europe, Latin America, and the Far East, so that today, in addition to the three hundred and fifty company-owned branches in the United States, Monroe distributors are located in all principal cities throughout the free world.

The extraordinary growth of the Company has been possible because the calculator filled a real need, and the Monroe Organization, besides introducing basic principles which are distinctive improvements in calculating machine equipment, adopted a program of education and service which continues to be successful to this day. From the time Mr. Monroe first conceived the idea of developing a machine to lighten the burden of office routine, figuring needs have been kept foremost in mind. Monroe research engineers have left nothing undone to produce instruments that fill computing requirements mechanically, electro-mechanically, or electronically.

From the very beginning, improvements in design have been adopted as fast as they were proved practical. It was not until the introduction of the K series in 1921, however, that any radical change was made in the appearance of the machine. This model, with its rounded corners and graceful lines, embodies still further mechanical improvements, yet retained the basic principles of the original Monroe. Under capable and determined supervision, the Monroe machine has been developed from the single model of 1917, cumbersome and clumsy in appearance, to the attractive, compact calculators of today, made in varied sizes and models.

Following the introduction of the hand-operated K machine came the electrically operated KA series. Various special machines were also introduced to handle special types of work, such as interest, fractions, British currency, etc.

Foreseeing the demand for a small, portable adding-calculator, the Company brought out its "L" series machines. The first one of this series which appeared in 1929 was the 7-1/2 pound Executive Monroe, the smallest calculating machine having a standard keyboard. This was later followed by the small electric LA-5 Monroe, which has the same size keyboard and is electrically operated. The most recent development in the L series is the new color coded LA-7 with automatic division.

In the MA series Monroe which followed, there was developed a quiet adding-calculator which combined with the features of other Monroe models, such additional advantages as the accumulating dials, split lower dials, and the half-cent dial. These permitted still further shortcutting of business problems and made possible the handling of large volumes of figure work even more quickly and economically.

Both the LA-5 and the MA machines were equipped with the "Spot-Proof" keyboard, which is claimed to be the greatest improvement made in keyboard design since the development of the first key set-up calculating machines.

The valuable educational work which has been undertaken by the Monroe Company has kept pace with the development of the Monroe machine. This educational program, which has been part of the policy of the Company since its inception, has been carried on and expanded under the direction of competent specialists.

The Company's educational department cooperates with its sales organization to aid business houses in the application of the Monroe machines to their particular figuring needs.

The Monroe Company's sales representatives, with their highly specialized training, may be considered figure experts, qualified to analyze the customer's figuring requirements and to recommend the best method of handling them. The accounting service departments at the Company's Orange offices is constantly at work on the figuring problems of every line of business. Most of its findings have been published in booklet form so that it is possible to obtain a course of instruction on the figure work of every major line of business.

In 1932, which marked the twentieth anniversary of the Monroe Company, its product was honored for the second time by the Franklin Institute. In the award of the John Price Wetherill Medal for improvements in design and construction which have been made on the Baldwin Calculator and incorporated in the Monroe Adding-Calculator, the institute has recognized a significant contribution to the progress of science in the perfection of a device which has already proved itself invaluable as an instrument of economy in the practical conduct of modern business.

More than 100 different styles of Monroe calculators have been manufactured to date. In 1929 the Monroe Company entered the Adding Machine Business and has since produced many varied models of Adding-Listing and Accounting machines.

Thus the Monroe Calculating Machine Company has accomplished much in the forty-five short years of its existence. The Company has had a definite influence on the conduct of modern business by removing the drudgery of office routine and eliminating the wastefulness and uncertainty of pad-and-pencil figuring methods. It is making a worthwhile contribution to business and industry through its simplification of figure work.

Paraphernalia

Miniature Cigarette Lighter

This is a cylindrical miniature cigarette lighter. Both ends are engraved with "Monroe Calculating Machine Co. Inc.", and its side has blue enamel with some red bands. Lifting off the cap reveals the wick and spark wheel. On the inside is engraved "Weston Intl. Corp., N.Y.C., Made in U.S.A.". This company made several kinds of lighters, often used as promotional items, and is likely to have been founded by Alexander Sydney Weston, who applied for and was granted several lighter patents in the early 1940s (US 2,318,037, US 2,331,445, US 2,358,955, US 2,372,238). Presumably then this lighter also dates from the 1940s.

Books, Manuals

Instruction Book Monroe Calculating Machine
Monroe Calculating Machine Co., New York
1919
48 page stapled book
177mm × 241mm

This is the manual for the Monroe calculator. It has a copyright year of 1919, which is when the model G was being produced. It describes addition, subtraction, multiplication, division, decimals, discounts, and interest, followed by oiling instructions and several tables. The main difference between handling the models D-G and later models is that to clear the register the carriage has to be manually lifted while turning the clearing handle. Later models lift the carriage automatically when the clearing handle is turned.

A later edition can be found below. A complete scan of this edition of the book can be found at Cris Vande Velde's site.

Instruction Book Monroe Calculating Machine    (PDF, 20.9 MB or archive.org)
Monroe Calculating Machine Co., New York
1922?
48 page stapled book
172mm × 235mm

This is the manual for the Monroe calculator, but a slightly later edition than the one above. It has no copyright year, but the code on the last page suggests it was printed in 1922, which is consistent with the fact that it discusses both the model G and the recently introduced model K. It describes addition, subtraction, multiplication, division, decimals, discounts, and interest, followed by several tables. The contents are almost the same as the previous version, except that the model K is shown in detail on the first pages, and to make room for that the setting up and oiling instructions have been omitted, and were provided in a separate loose set of pages.

Instructions for Setting Up and Oiling the Monroe Calculating Machine    (PDF, 1.92 MB or archive.org)
Monroe Calculating Machine Co., New York
1922?
4 page folded sheet
177mm × 241mm

This is a loose supplement to the instruction manual above which shows you how to set up the calculator for first use (attaching the carriage and cranks) and how to oil it. It applies to the model K calculator and the older model G machine.

The Monroe Calculating Machine (Office Machine Practice)    (PDF, 16.2 MB or archive.org)
Chester H. Katenkamp
The Gregg Publishing Company
1931
58 page stapled book
142mm × 204mm

Chester Katenkamp wrote a series of four Office Machine Practice booklets, of which this is the one for the Monroe. The others were for the Comptometer, the Burroughs calculator, and the Sundstrand machine. It is essentially a manual, explaining the four arithmetic operations, fractions, discounts, chain discounts, and decimal points.

This book is in good condition, partly because the centre pages have been strengthened with tape along the spine to prevent the staples from tearing through, and similarly there is tape along the spine on the outside of the cover. The name of the original owner is written on the title page, but the book is otherwise clean.

Monroe Machine Methods For the Extraction of Square Root    (PDF, 5.07 MB or archive.org)
Monroe Calculating Machine Company, Inc.
1933
11 page stapled booklet
150mm × 229mm
Form 769-S

This booklet explains how to take square roots when using the Monroe calculator.

Monroe Machine Methods For the Extraction of Cube and Other Roots    (PDF, 3.90 MB or archive.org)
Monroe Calculating Machine Company, Inc.
1933
8 page stapled booklet
149mm × 228mm
Form 720 S

This booklet explains how to take cube or higher roots when using the Monroe calculator. It uses Newton's Method to get successively better approximations.

It does not have a copyright year inside, but the similar booklet for the square root refers to this one, so it is presumably from the same year, 1933.

Instruction Book Monroe Adding-Calculator LA Models    (PDF, 16.5 MB or archive.org)
Monroe Calculating Machine Company, Inc.
1947
40 page stapled book
153mm × 228mm × 2mm

This is the 1947 manual for the Monroe calculator, specifically the model LA-X and the Series 0 models.

Monroe Octal Calculator The Machine and What It Does    (PDF, 2.93 MB or archive.org)
Monroe Calculating Machine Company, Inc.
1950?
8 page stapled booklet
152mm × 228mm

This booklet introduces the Monroe Octal Calculator, a version of the LA5-200 that counts using base 8, which was intended for engineers of electronic binary computers.

Advertisements and Articles

Advertisements

I found many advertisements in online archives of newspapers and magazines. They are too numerous to show here, so they can be found on a separate Monroe Advertisements page.

Articles

Here are a few articles taken from various online archives.

Frank Baldwin is director of newly founded Monroe
(1911-10-19, Brooklyn Times Union (New York))

Monroe lease factory formerly belonging to Pike
(1913-04-26, Newark evening star and Newark advertiser)

Monroe at Washington's annual business show
(1914-10-13, The Washington Times (Washington DC))

Monroe at Greenville's textile expo
(1915-11-02, The Greenville News (South Carolina))

Exhibit of the Monroe Calculator
(1916-09, Pacific Municipalities)

Early biographies of Jay Monroe and Frank Baldwin.
(1918, The National cyclopaedia of American biography)

About Jay Monroe, his company and its culture.
(1919-04, National Magazine)

Sponsored article promoting the Allen car used by a Monroe salesman.
(1920-04-18, Arizona Republican)

Automatic Calculation
(1920-06-02, Pall Mall Gazette)

City Offices and the Monroe
(1920-12, The American City)

Description of the Monroe
(1921, Illustriertes Orga-Handbuch erprobter Büromaschinen, Ludwig Brauner and Victor Vogt)

Biographies of Jay Monroe and Frank Baldwin.
(1922, The History of the Oranges to 1921)

Jay R. Monroe going on a European tour.
(1922-03-09, The Michigan Alumnus)

Monroe donates series of calculators to the National Museum.
(1922-05-06, The Washington Herald)

Monroe calculators used in counting election results
(1922-11-11, The St Louis Star and Times (Missouri))

Portable Automatic Model Calculating Machine
(1923-03, Railway Mechanical Engineer)

An Automatic Calculating Machine
(1923-04, The American City)

Description of Monroe calculators.
(1925, Die Rechenmaschinen by Ernst Martin)

Advert for LaSalle Extension University, focussing on a Monroe district manager.
(1926-09, Popular Mechanics)

Biography of Frank Baldwin.
(1928, Dictionary of American biography)

Monroe at the Business Efficiency Exhibition.
(1929-09-10, The Sydney Morning Herald)

Monroe-Rechenmaschine
(1930, Organisations-Lexikon by Walter le Coutre and Walter Thoms)

Patents

The Monroe company filed a large number of patents on every detail of the calculators. I have therefore cut this list off at 1935, leaving off the 170 or so patents that followed in the next 35 years.

Links

• Monroe Systems has a page on the history of the company, including interviews with Frank Baldwin and Jay Monroe.
• John Wolff's Web Museum has a Monroe page.
• rechenmaschinen-illustrated has a Monroe page.
• rechnerlexikon has a Monroe page.
• Cris Vande Velde has pages for the Model F, Model G, Model K, and an unusual Model K for British currency.
• Computer Timeline has a page about Frank Baldwin's pioneering work before the Monroe machines.
• Mechanicalcalculators.wordpress.com has a Monroe page.
• IFixIt has a disassembly guide for the Monroe LA, but it is only the carriage and main register for now.
• Archive.org has a collection of documents from the Monroe company, including notes to service engineers.
• The Id of Ed is a youtube channel that has videos about restoring a Monroe model K, model LA, and a model CST 8.
• bss1250 on YouTube has many videos about restoring calculators, including a Monroe model D (D 858).
• National Museum of American History has many Monroe machines, including an early D, D, E (incorrect picture), F, G, K200, KA160, K121, K160 with braille, KA120, LA5-160, LA-200, LA5-160x, CSA8, 8N-213, 8N-213, IQ-213, and CSAE-10.

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