While it's hard to beat the aesthetic appeal of the Burroughs Class 1 and 3, they are big, heavy, and slow. If you don't need a paper record you'd be better served by its 1919 competitors the Comptometer Model F or Monroe Model G I featured here earlier.

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You multiply by repeated addition in the ones column, then shift left and repeat for each digit in the multiplicand. Normally the keys reset when you pull the lever, but by pressing the repeat key they stay down until you press the Total key. Here is 12 x 12.

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This is an adding machine--it only adds. To subtract, you have to use the complements method. For instance, to subtract 42 from 31342, I convert 42 to its complement (99999958) and add it. The carries shift off the left of the register and the difference remains.

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To add, enter the first number in the keyboard and then pull the lever to add it to the register and print it on the tape. The enter the second number and pull the lever again. The lever provides the force necessary to print. Here's 31337 + 5.

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The Class 3 is a rather different design from the Class 1. Like tech companies today, Burroughs expanded by buying competitors. This machine was originally made by the Pike company in 1909 which Burroughs bought in 1911 and it became a core part of a larger product line.

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This is a Burroughs Class 3 adding machine from 1919. Where the Class 1 I featured here earlier has fancy beveled glass and a full carriage on the back to accept ledgers, this later Class 3 has a simple paper spool and was used for general accounting.

"It is manufactured by our "special process" which leaves the *individual molecules unscathed*, retaining the "rubber-ball" springiness of the oil."

While they aren't as pretty as Burroughs adding machines, Comptometers are *fast* and functional (you can calculate square roots on them!) and are my favorite from this era. There's a reason they stuck around with only minor tweaks until the age of electronic calculators.

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This red button is part of the control key mechanism. Operators touch-typed, and partial key presses would increment the register only partway. If you press a key part-way down, all other columns lock until you go back and fix that column and press the red button to clear.

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To clear the register, pull the lever back then forward. It makes a satisfying noise when the register clears or carries. This was designed for mostly one-handed operation and future revisions just require you to pull the lever forward to clear.

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You do division w/ repeated subtraction using small digits (minus one!) starting from the left, shifting right when leftmost digit in dividend is 0. You don't use the front switch so that carried digits form the quotient in the register. Here is 145 / 12 = 12 remainder 1.

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Multiplication is easy and fast. Just do repeated addition for the first digit in the multiplier and shift left until each digit is accounted for. Here is 768 x 1024.

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To subtract, use the small digits on the keys instead of the large, subtract one from the subtrahend, and hold down the correct switch in the front to prevent the one from carrying. To do 31342 - 42, I press 41 in small digits (58 in large digits) while holding the front switch.

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Like with other Comptometers, you just press corresponding keys to add. Trained Comptometer operators performed calculations by feel (odd keys were concave, even were flat) and mostly one-handed so their eyes and left hand could stay on the sheet of figures. Here's 31337 + 5.

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The Comptometer to the right is a Model F, made between 1919 and 1920. It is the mass-produced successor to the smaller (and rarer) Model E (1913-1914) to the left. The Model E introduced a "control-key" mechanism to prevent errors from half-presses, but Model F simplified it.

I'm not add-icted. I can subtract whenever I want. Of course to subtract I would need to add something complementary...

The Burroughs adding machines aren't my favorite to use, but they are my favorite to look at. Check out the lines on this 100-year-old Class 3. It reminds me of sedans from that era.

As I mentioned the Model C was designed for Imperial measurements and had a dial that went up to 11 so inches could carry over into feet. Here I'm calculating 2' 9 3/4" + 1' 6 7/8". Doing math with Imperial measurements really makes you appreciate the Metric system.

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You can also perform division using the repeated subtraction method but you have to keep track of the number of subtractions in your head. To clear the registers, just pull on the lever on the right side. This also ejects the stylus for you if it's in storage.

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