Monroe Calculating Machine (G Model)


Accession Number: 2019.ast.111.1-2 (DAA-0044)


The main part of this object (2019.ast.111.1) is a black metal box with a number of keys on the front, arranged in an ascending formation, with a row of short 0 keys at the front and a row of tall 9 keys at the back, with the other numerals in between. A single red key is set to the right to this, alongside a metal knob with an arrow on the top. On the right side of the box there is a rotating crank handle. On the front side of the box there is a key-type knob which when rotated lifts the display carriage and moves it to the left or right by one digit.

Behind the keys, mounted on the back edge of the top of the box, there is a wider section, the carriage, containing the display of the calculating machine. This is has two rows oval holes through which numerals are visible. On the right hand side of the carriage there is a rotating crank handle (the reset knob), and a knob (to lift the display in order to reset the displays). Along side the numerical displays there are metal indicators which can be slid along a numbered rail to indicate specific numerals.

There is a Instruction Book with this object (2019.ast.111.2). This contains instructions on the use and care of the machine.

Alternative Name: Mechanical Calculator

Primary Materials: Metal: Iron Alloy, Plastic


Painted on the front of the box: “MONROE
Calculating Machine Company
New York, U.S.A.

Painted on the back of the box: “MONROE

Dimensions (cm):

Length = 44, Width = 33.4, Height = 16.5


To aid simple calculation, including addition, subtraction, multiple and division.


Good: The calculator (2019.ast.111.1) shows many signs of use. The keys, crank handles and other surfaces frequently touched during use are worn and dirty. The painted-on label is worn in places. The metal surface of the box and display carriage is rusty in placaes, particularly around the corners.

The booklet is in very good condition. It is slightly worn on the cover and the paper is yellowed, but is in otherwise undamaged.


Monroe Calculating Machine Company, Orange, New Jersey

Date of Manufacture: 1919-1921


This object was moved from the David Dunlap Observatory in Richmond Hill in 2009, upon the sale of the observatory. They were stored at the Department of Astronomy and Astrophysics until 2017, when it was moved to a new storage location in McLennan Physical Laboratories.