Mechanical calculators: Burroughs Class 5

* Back to Offline Hours

* Back to Mechanical Calculators

This machine was manufactured by Burroughs in the United States, in Detroit, Michigan, in 1926 (see here). I bought it at an online auction site, in May 2019, from just two posted images. I took the chance of buying it without being able to see much of the machine's condition, but this one is older, rarer in Brazil, and has a simpler mechanism, based on the Comptometer.

Online sources say that Burroughs was sued for nearly copying the Comptometer's working mechanism in other machines, and then came out with the Class 5 with a few innovations, including a more compact design, aiming at desktop use. Earlier bulky Burroughs adding machines were mounted on pedestals and placed at the center of offices, to be shared among many operators.

My unit has seven missing keys, and one white “3” key too many. This was probably a replacement taken from another machine. It was locked and unresponsive, the painted aluminum alloy (?) case sprinkled with white paint specks, and all rubber feet crumbling away. The decimal point indicators are also missing. Two of the display's numbered wheels are cracked, one badly and slipping from its position. Those must be glued back in position to work.

Online photos of museum units and other well-preserved Class 5s show, right to left, two columns of white keys, three blacks, three whites and one black. This points to adding money figures, up to 9,999,999.99. My unit has, right to left, three black columns, three whites, and three blacks. This is probably due to the Brazilian currency prior to 1942, called “réis” (plural of “real”). A single real back then was basically worthless, so money units were called “mil-réis”, for thousand reais, and denoted like 1.000$000. Three groups of three columns then make more sense than having two columns for cents, which we did not have back then. The smallest denomination was a 20 réis coin, dubbed the “vintém”. The 100 réis coin was called a “tostão”, and the highest denomination was worth 1.000$000, or a thousand mil-réis. A million réis was called a “conto de réis”.

As essentially a Comptometer, this machine does not actually add fully input numbers to an accumulator on command. The lever to the right is only used for clearing. As keys are pressed and released in each column, the mechanism immediately advances the corresponding digit by the required number of positions, and then carry flows to the digit to the left. The operator never actually sees the number being added anywhere: not in the display, nor as a set of down-pressed keys. The effect of each typed-in digit is immediate, so recognizing and correcting mistakes must have been painful. On the other hand, digits can be input simultaneously, by pressing keys in different columns at the same time – weird. Also, the effect of pressing, say, 2 and then 5 in a column is the same as pressing a 7 in the same column, but 2 + 5 require less arm and wrist movement. As a result, keys from the bottom rows show much more wear than keys in the top rows. Later machines based on the same principle have only 5 rows of keys, requiring double keypresses to input larger digits.

It is interesting to notice that adding columns of numbers can be done column-wise, giving the same result. Say you need to add 123 + 456 + 789. You can type in 3 - 6 - 9 on the rightmost column, then 2 - 5 - 8 on the second, and 1 - 4 - 7 on the third, much like adding manually.

Subtracting in the Class 5 is, as in the Comptometer, also troublesome. The operator is required to enter a tens-complement number, using preceding 9s and typing the number to be subtracted by looking at the small numbers on the keycaps. The preceding 9s are actually zeroes if you look at the small numbers in the keycaps. Oh, and the subtrahend must be reduced by one so the tens-complement works correctly. Whew. More on Burroughs Class 5 operation here.

My plans: make it work smoothly, which does not seem to be a difficult proposition, then repaint everything, including the numbers on the keytops. I'll also try to produce a stylish Burroughs logo from online photos – mine only has a small fragment of the logo left. Missing keytops can be 3D-printed, and the rubber feet should be easy to replace. I'll also look into designing the longer back feet (possibly an optional accessory) as in some online pictures, and have them 3D printed as well.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

1926 Burroughs Class 5 s/n 5-1065827

As purchased

 As purchased

More about this machine

John Wolff shows a wider Class 5, with 13 columns instead of 9, including a column for Sterling currency units

Video: a demonstration of the Class 5 in action

An operations description, including an explanation on subtraction modes and their special cases

A beautifully preserved unit at the UK's Science Museum

A time-lapse video of an artist recreating the shape of a Class 5 using only a photo and a 3D design software package

Instructions for Operating the Burroughs Calculator. 36 page booklet

Back to top
burroughs_class_5.txt · Last modified: 2019/05/17 22:32 by clodoveu
Recent changes RSS feed Creative Commons License Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki