Monroe High Speed Adding Calculator (LA5-160x)

Monroe High Speed Adding Calculator (LA5-160x)

Mathematics; Business; Physics; Engineering

Physical Description

The calculator generally comprises three main parts: the main housing, the keypad, and the output carriage.

The main housing for the calculator is rectangular as seen from the top, with one pale green slanted face on the front where the keypad is located, similar to a typewriter or cash register. The main housing is a shiny dark green in color with the appearance of a scale-like texture. On the bottom of the main housing are four feet which are steel with a rubber boot. On the front of the main housing, just below the slanted face, a "T" shaped knob protrudes. The knob has a small polished aluminum shaft (15mm long, 6mm diameter) with small black enamel handles (12mm long). Then, on the face to the right of the slanted face (when viewed straight on as if operating) is a knurled aluminum knob about 25mm in diameter. On the back of the calculator (opposite the slanted face) is an electrical connector that is on the right side of the calculator. Lastly, there are "MONROE" logos with yellow letters outlined in red on the front face below the slanted face and centered on the back, under both of which there are the words "HIGH SPEED ADDING CALCULATOR" in yellow. The logo on the back is much larger, while the logo on the front is about half the size and positioned towards the right. Additionally, on the bottom of the calculator in the center is a yellow tag that has the same logo in black letters with additional product information writtten below it.

Housed on the slanted face is the keypad. This pale green panel contains a 10x8 array of white buttons (6mm diam.) with black numerals, 0 through 9. Each column starts with a zeroing key at the bottom and increases to nine at the topmost row. To the right of the number pad is another column of various buttons. Starting at the top is the subtraction button (with an inscribed - symbol) which is long, rectangular (35mm long, 13mm wide), and black in color. Directly below that is the addition button (with an inscribed + symbol) with the same shape, orientation, and color. Under that is a 6mm diameter red button that has no symbol. Then under that is another 6mm diameter red button with a darker red "R" on it. Last below that button is a larger red button (14mm diameter) with a pale green zero. The final component on the front panel is a small aluminum lever directly to the left of the left-most "1" button that stands 10mm tall.

At the top rear is the output carriage. The carriage is primarily the same dark shiny green as the main body. The carriage is a triangular prism in shape with one of the long flat faces facing the operator, which is at the same angle as the input panel. On this primary face are two rows of small windows (5mm tall and 4mm wide). The bottom row closest to the number pad consists of 16 windows, while the top row consists of 8 windows that are directly above the eight rightmost widows of the bottom rows. Inside each of the windows are black numbers (on the top row, there is also a set of red numbers for subtraction) on a white roller much like a slot machine. Directly above the lower set of windows is a rail with yellow numbers above each window, starting with one on the left and ending with 16 on the right. Along this rail is a set of 5 brass sliders with very small knobs (3mm diameter) that are attached to red arrows that point down towards the lower set of windows. Directly above this rail and below the upper set of windows is another shorter rail that matches the shorter number of windows. This rail has eight numbers and one slider that points upwards. A large steel knob (15mm in diameter) is to the right of these rails. Lastly, on the right face of the carriage is a crank with a dark wooden knob about 10mm in diameter with a polished aluminum arm (20mm long).

Functional Description

The purpose of this calculator is complete simple arithmetic such as adding, subtracting, multiplying, and dividing.

Before doing any calculations, users will need to reset the registers (number windows on the carriage). Operators can do this by rotating the crank attached to the carriage until the register reads zero.

For adding, users type in the first number into the keypad by depressing the corresponding buttons, where the number furthest to the right is the smallest digit (which could represent a decimal). Then, the user shall click the plus button causing an electric motor to spin and load the number into the lower register (the longest set of windows). After that, users type the next number to which they would like to add in the same manner. Then, after selecting the add button, the value in the lower register will be the sum that the user is looking for.

For subtracting, the user should perform a similar process where they type in the larger of the two numbers and then press the add button to add the larger value to the register. After that, operators should input the subtracting value into the keypad. Then the user shall select the subtraction key, causing the motor to spin in the opposite direction. This will yield the desired difference in the lower register.

For multiplication, the user must input the larger value into the number pad. The operators shall select the red key with an R. This locks the number so that after the addition key is selected, the number pad will not reset. If the small number of the multiplication is less than ten, the user shall select the addition key as many times as the smaller number. The upper register will count the number of times the user has selected the addition key, and the lower register will display the product.

If the smaller number happens to be larger than ten, the user can select the add key for the smallest digit of the smaller number, and then they can shift the entire carriage with the T-shaped knob so that they add to the power of ten more. Operators should repeat this process until the upper register shows the smaller number of the multiplication, and the resultant in the lower register will be the product.

Operators can perform division in the same manner as a multiplication; however, they shall input the larger number into the lower register. Then, they can use the subtraction key instead of the addition key until the lower register reads as close to zero as possible (remainders may exist). The operator can then read the result of the division in the upper register in red numbers.

In addition, the calculator has some extra useful functions. One is at the bottom of each column is a zeroing button which can be used to clear a column if the incorrect value is selected. Similarly, there is a larger read zeroing buttons that clear the whole number pad. Another feature is a small lever that users can move to hold down the leftmost one on the number pad. This will cause the leftmost digit in the register to count the number of additions or subtractions performed. Another functional feature is the set of sliders on the registers. Ultimately, these sliders are used for the reference of the user and are often used for dealing with decimal numbers where the digits furthest to the right are the smallest decimal value or unit of precision. Lastly, there is a knob on the right side of the calculator that can be used to spin the motor and perform calculations without electricity. In this case, the knob shall be rotated clockwise to add and counterclockwise to subtract.

Isaac Couling

1940-1950

English

Physical Object

no accession number

United States of America

[Main Body] 180 mm wide x 285mm deep x 175mm high
[Output Carriage] 290mm long x 55mm high x 50mm deep
[Number Pad] 114mm wide x 140mm high
[Number Button] 6mm diam x 6mm high
[Plus/Minus Buttons] 13mm wide x 35mm high
[Red Zero Button] 6mm diam x 6mm high
[Small Red Buttons] 6mm diam x 6mm high
[T-Knob] 15mm long x 6mm diam x 12mm long handle
[Aluminum Knurled Knob] 25mm diam
[Aluminum Leveler] 10mm high
[Carriage Window] 4mm wide x 5mm high
[Steel Knob] 15mm diam
[Crank] 10mm wooden knob diam x 20mm long aluminum arm

Steel, Aluminum, Plastic (Bakelite), Copper, Rubber, Wood

Monroe Calculating Machine Company, in Orange, New Jersey

[Front Logo] MONROE | REGISTERED TRADE MARK [Rear Logo] MONROE | REGISTERED TRADE MARK | HIGH SPEED ADDING CALCULATOR
[Rear Serial Number] MCMT-4590
[Bottom Label] MONROE | CALCULATING MACHINE COMPANY | NEW YORK, USA | NO. 1 | 100-135 VOLTS D.C.

Although the history of this specific object in the Mechanical Engineering department has yet to be discovered, based on its function, it had the potential to be useful for several tasks. For example, engineering requires a lot of data collection and analysis. As a result, it can be assumed that this calculator aided engineers in data analysis, which may have required simple repetitive arithmetic that this calculator could perform more quickly than an engineer could do by hand. Additionally, this calculator could have aided mechanical engineers in advanced calculations. While this calculator cannot do calculus or solve differential equations, it can perform numeric approximation for such calculations. Such numeric approximation would have been based on Euler's method or Newton's method of approximation. Both methods involve repeating many sets of basic arithmetic that, if performed at small enough intervals (which requires many calculations), could produce accurate approximations of complex math problems.

Mechanical Engineering and Engineering Mechanics building 3rd-floor display case.

“Monroe Model LA5-160X Calculating Machine.” National Museum of American History. Smithsonian, 2023. https://americanhistory.si.edu/collections/search/object/nmah_690151.

MONROE CALCULATING MACHINE COMPANY. INTRUCTION BOOK Monroe Adding-Calculator LA-Z or Series 0 Models. Orange, New Jersey: 1947.

Scherphuis, Jaap. “Jaap's Mechanical Calculators Page.” Monroe Calculating Machines -
Jaap's Mechanical Calculators Page, 2016.
https://www.jaapsch.net/mechcalc/monroe.htm#mymodelka.

Wolff, John. “The Monroe Calculating Machine Company.” John Wolff's web museum, December 8,
2017. http://www.johnwolff.id.au/calculators/Monroe/Monroe.htm.