Jaap's Mechanical Calculators Page

Monroe Calculating Machines

Monroe Model K-160 Monroe Model KA-160 Monroe Model L-200X

My Model K
My Model KA
My Model L
How to use the Monroe
Books, Manuals
Advertisements and Articles

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 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.

Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160

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.

Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160
Monroe K-160

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.

Monroe KA-160
Monroe KA-160, rear
Monroe KA-160, keyboard
Monroe KA-160, logo
Monroe KA-160, motor label
Monroe KA-160, opened, top
Monroe KA-160, opened, left
Monroe KA-160, opened, rear
Monroe KA-160, opened, right
Monroe KA-160, serial number
Monroe KA-160, opened, carriage
Monroe KA-160, opened, planetary gears

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.

Monroe L-200X
Monroe L-200X, top
Monroe L-200X, front
Monroe L-200X, right
Monroe L-200X, back
Monroe L-200X, logo
Monroe L-200X, left
Monroe L-200X, bottom
Monroe L-200X, crank
Monroe L-200X, crank
Monroe L-200X, keyboard
Monroe L-200X, keyboard
Monroe L-200X, register
Monroe L-200X, shifter

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.

Monroe L-200X, carriage
Monroe L-200X, carriage
Monroe L-200X, mechanism
Monroe L-200X, stepped drums
Monroe L-200X, crank
Monroe L-200X, shifter
Monroe L-200X, rear
Monroe L-200X, serial number


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

How to use the Monroe

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.

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.

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.

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.

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.

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

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.


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. Very little is known about models A, B, and C, as few of them were made, and possibly none are 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 there are separate clearing handles for the counter and register. Larger scale production started with the model D in 1915. This was followed by the models E, F, and G over the next four years. These were increasingly successful, but are relatively rare today. There are no known machines of models H, I, and J, as these models were not put in production.

The model K was released in 1921, and produced through most of the 1920s. It was commercially very successful, even though 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 models followed, most of them electrically driven. They also produced many listing calculating machines.

Here is a table listing the calculator models.

ModelYearSerial NumbersCharacteristics
A,B,C1911-1914?Boxlike case; Drive gears on outside; two clearing handles; repeat/non-repeat knob; carriage has row of pins fitting into one slot above keyboard; no item count knob; no keyboard column markers
D19151,000?-1,749Drive gears inside case; one clearing handle; item count knob; keyboard column markers
F1917-19186,000-10,564Carriage has one pin slotting into comb above keyboard
G1919-192020,000-38,542Carriage automatically lifts when clearing register
K/KA1921-192958,557-144,100Repeat/non-repeat buttons; rounded case; comb moved to shifting mechanism

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:



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.

Books, Manuals

Instruction Book Monroe Calculating Machine
Monroe Calculating Machine Co., New York
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 F 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 model F 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 complete scan of the book can be found at Cris vande Velde's site.

Monroe Instruction Book, front cover
Monroe Instruction Book, title page
Monroe Instruction Book, foreword
Monroe Instruction Book, part I
Monroe Instruction Book, index

The Monroe Calculating Machine (Office Machine Practice)    (PDF, 16.2 MB)
Chester H. Katenkamp
The Gregg Publishing Company
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.

Office Machine Practice - The Monroe Calculating Machine, front cover
Office Machine Practice - The Monroe Calculating Machine, title page
Office Machine Practice - The Monroe Calculating Machine, index
Office Machine Practice - The Monroe Calculating Machine, pages 2 and 3
Office Machine Practice - The Monroe Calculating Machine, pages 26 and 27

Monroe Machine Methods For the Extraction of Square Root    (PDF, 5.07 MB)
Monroe Calculating Machine Company, Inc.
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 Square Root, front cover
Monroe Machine Methods For the Extraction of Square Root, title page
Monroe Machine Methods For the Extraction of Square Root, first page
Monroe Machine Methods For the Extraction of Square Root, last page
Monroe Machine Methods For the Extraction of Square Root, back cover

Monroe Machine Methods For the Extraction of Cube and Other Roots    (PDF, 3.90 MB)
Monroe Calculating Machine Company, Inc.
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.

Monroe Machine Methods For the Extraction of Cube and Other Roots, front cover
Monroe Machine Methods For the Extraction of Cube and Other Roots, first page
Monroe Machine Methods For the Extraction of Cube and Other Roots, last page
Monroe Machine Methods For the Extraction of Cube and Other Roots, back cover

Instruction Book Monroe Adding-Calculator LA Models    (PDF, 16.5 MB)
Monroe Calculating Machine Company Inc.
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 Instruction Book, front cover
Monroe Instruction Book, title page
Monroe Instruction Book, diagram
Monroe Instruction Book
Monroe Instruction Book, back page
Monroe Instruction Book, back cover

Advertisements and Articles


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.


Here are a few articles taken from various online archives.

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

1918 The National cyclopaedia of American biography
1918 The National cyclopaedia of American biography
1918 The National cyclopaedia of American biography
1918 The National cyclopaedia of American biography

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

1919-04 National Magazine 1
1919-04 National Magazine 1
1919-04 National Magazine 1
1919-04 National Magazine 1

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

1920-04-18 Arizona republican

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

1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921
1922 The History of the Oranges to 1921

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

1922-03-09 The Michigan Alumnus

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

1922-05-06 The Washington herald

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

1925 Ernst Martin
1925 Ernst Martin
1925 Ernst Martin
1925 Ernst Martin
1925 Ernst Martin
1925 Ernst Martin

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

1926-09 PopularMechanics

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

1928 Dictionary of American biography

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

1929-09-10 The Sydney Morning Herald


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.

PatentFiling datePriority dateNameDescription
US 890,88824-01-190716-06-1908Baldwin, Frank S.Calculating machine
US 1,080,24515-06-191202-12-1913Baldwin, Frank S.Calculating machine
US 1,180,41004-06-191425-04-1916Monroe, Jay R.; Phinney, Edgar E.Carriage-shifting means for calculating-machines
US 1,197,53804-12-191405-09-1916Phinney, Edgar E.Carrying mechanism for calculating machines
US 1,207,70024-02-191512-12-1916Baldwin, Frank S.; Baldwin, George H.Calculating Machine
US 1,208,19025-09-191412-12-1916Monroe, Jay R.Carriage-lock for calculating-machines
US 1,208,36627-10-191412-12-1916Phinney, Edgar E.Spring brake for gears
US 1,215,18603-08-191406-02-1917Phinney, Edgar E.Carrying Mechanism for Calculating Machines
US 1,272,08327-08-191509-07-1918Phinney, Edgar E.Carrying mechanism for calculating machines
US 1,275,11924-09-191406-08-1918Baldwin, Frank S.Zero setting mechanism
US 1,335,34908-04-191930-03-1920Phinney, Edgar E.Automatic carriage raising means for calculating machines
US 1,354,83908-03-191705-10-1920Phinney, Edgar E.Keyboard clearing means for registers
US 1,358,51715-03-191909-11-1920Burne, James C.Attachment to adding-machines
US 1,384,59214-04-192012-07-1921Britten, Edwin F.Shock-absorber for calculating-machine carriages
US 1,384,63225-02-192012-07-1921Phinney, Edgar E.Key lock for calculating machines
US 1,384,63328-02-192012-07-1921Phinney, Edgar E.Reverse operation check for registers
US 1,384,63407-02-192012-07-1921Phinney, Edgar E.Carriage-lock for Calculating-machines
US 1,396,61223-10-192008-11-1921White, NelsonZero setting mechanism
US 1,396,66226-12-191808-11-1921Phinney, Edgar E.Calculating machine
US 1,396,66315-03-192008-11-1921Phinney, Edgar E.Crank-handle latch
US 1,432,25603-06-191917-10-1922Phinney, Edgar E.Calculating Machine
US 1,432,61608-03-192017-10-1922Phinney, Edgar E.Keyboard clearing means for calculating machines
US Re 16,20721-09-192310-11-1925Phinney, Edgar E.Keyboard-clearing means for calculating machines
US 1,462,05814-04-192017-07-1923Britten, Edwin F.Carry Mechanism for Registers
US 1,462,05903-08-192017-07-1923Britten, Edwin F.Automatic carriage raising means for calculating machines
US 1,462,06023-11-192017-07-1923Britten, Edwin F.Carry set mechanism for calculating machines
US 1,462,06123-11-192017-07-1923Britten, Edwin F.Overthrow check for calculating machines
US 1,544,80616-01-192207-07-1925Chase, George C.Full cycle stop for calculating machines
US 1,664,66107-11-192503-04-1928Chase, George C.Full cycle positioning mechanism
US Re 18,13018-03-193021-07-1931Chase, George C.Full cycle positioning mechanism
US 1,685,07415-03-192618-09-1928Chase, George C.Multiplier mechanism for calculating machines
US Re 17,46607-08-192922-10-1929Chase, George C.Multiplier mechanism for calculating machines
US 1,750,56522-09-192511-03-1930Britten, Edwin F.Zero key machanism for key set registers
US 1,773,02503-10-192712-08-1930Chase, George C.Carriage-shift control for calculating machines
US 1,773,02615-10-192712-08-1930Chase, George C.Carriage-shifting mechanism for calculators
US 1,773,02712-08-192912-08-1930Chase, George C.Calculating machine
US 1,781,32010-04-192911-11-1930Crosman, Loring P.Zero setting device
US 1,794,51406-04-192903-03-1931Chase, George C.Driving mechanism for calculating machines
US 1,801,48426-02-193021-04-1931Bricken, JohnKeyboard for calculating machines
US 1,805,06024-06-193012-05-1931Walter, Edward C.Calculating machine
US 1,805,06122-07-193012-05-1931Walter, Edward C.Register
US 1,829,21005-01-192727-10-1931Chase, George C.Automatic Carriage Shifting Mechanism for Calculators
US 1,849,44802-02-192915-03-1932Britten, Edwin F.Registering Mechanism
US 1,877,80129-05-193020-09-1932Britten, Edwin F.Calculating Machine
US 1,877,80213-02-193220-09-1932Britten, Edwin F.Calculating Machine
US 1,883,76022-04-193118-10-1932Bricken, JohnCalculating Machine
US 1,911,79623-07-193130-05-1933Brown, Lee R.Register
US 1,929,05313-06-193103-10-1933Brown, Lee R.Register
US 1,964,21122-09-193226-06-1934Overbury, Austin A.Calculating Machine
US 1,965,87913-03-193410-07-1934Britten, Edwin F.Calculating Machine
US 1,968,12328-02-193131-07-1934Bricken, JohnCalculating Machine
US 1,974,52920-04-193125-09-1934Brown, Lee R.Register


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.
History of Computers 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.

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