Kyle Rankin @kyle@librem.one

The chain only moves in one direction, so to subtract you have to use the complements method. To subtract 42 from 31342, I add 9999958.

These are portable, but are bigger and heavier than other pocket calculators of the time and primarily sat in or on a desk using the kickstand, and were used for quick arithmetic. To add a number, insert a stylus at the corresponding digit and drag down to the bottom.

These are known as chain adders. By inserting a stylus and dragging the chain down, you increment the register. You can see the carry mechanism in this video, which uses a spring-loaded tooth that rides along the outside of the gear and engages with the next gear only after 9.

These are Golden Gem portable adding machines made by the Automatic Adding Machine Company. The chrome one on the left was made around 1910 and the black one on the right, which has its original box, case, warranty card and receipt, was purchased in February 1941 for $9.16.

Division aside though, this is my favorite lever style adding machine in my collection to use, due to the subtraction key and overall key placement that enables one-handed operation. I could actually see myself using this to balance a checkbook if I still did that sort of thing.

Multiplication is repeated addition, shifting left for each digit in the multiplier, like other lever adding machines. By pressing down the repeat key the keys stay depressed after you pull the lever so you press the Correction key to release them and shift left. Here is 12 x 12.

You can hold down the subtotal button and pull the lever to print the current total without clearing the register, or you can hold down total to clear the register and print the total. This design is nice in that you can do it all one-handed.

This machine does have one fancy feature: a subtraction button! Instead of the complements method, you can just enter the subtrahend, hit the subtract key and pull the lever. Subtraction prints in red ink! Here I perform 31342 - 42 slowly so you can watch the counter.

Back to the Model 75. To add, enter the first number in the keyboard and pull the lever to add it to the register and print on the paper tape. Then enter the second number and pull the lever again.

It wasn't until the 1950s that trends changed and popular office machines started having green and grey hues, like this early 1950s NCR 11-EN. One big exception was the Comptometer, which kept its brown tones until the 50s when it too shifted to the green/grey aesthetic.

The Burroughs Class 3 I showed earlier in the thread is an example of rebranding a machine originally made by the Pike company. But when 90% of a market looks a certain way, competitors (like this Monroe Model G from 1918) mimic the design. So even in 1946 RC Allen followed suit.

At one point Burroughs controlled about 90% of the adding machine market. It accomplished this like companies today: it bought up its competitors and rebranded their products. That meant painting them black, and instead of felt, they just painted the spot under the keys green.

The Burroughs Class 1 was the first adding machine Burroughs sold starting at the end of the 19th century. It was the Cadillac of adding machines and featured a shiny black case, beveled glass on the sides to show off the mechanism, and actual green felt under the keyboard.

This machine looks and functions largely the same as Burroughs adding machines 30-40 years older. Have you noticed how many machines I've featured (like this Burroughs Class 3) have a black case, and a keyboard with white and black keys on a green background? My theory for why:

This is an RC Allen Model 75 adding/listing machine from around 1946. RC Allen was founded in 1932 in Grand Rapids Michigan and was a distributor of Facit calculators from Sweden. The brand still exists today as a manufacturer of precision aircraft instruments.

Ok I think we are ready for tomorrow.

I fixed the timing but this is as clean as I dare to make it right now. It got wet in storage some time in the past and rust worked its way under the black paint and through part of a screw. The rest of the paint is very flaky. I removed as much surface rust as much as I dared.

Round 2. This time with a Gem portable adding machine from 1941 (I have the original box, receipt, and warranty card) that's rusty *and* has two digits out of time with the rest of the register.

Done! One reason I cleaned it is I smelled that "old appliance" smell and wanted to ensure the motor wasn't strained. I ran it with the cover off and saw flashes in the back. The mechanism disconnects the motor when it's not needed, and that makes it arc. I was smelling ozone!

Time to clean and oil (and this time not have to repair) a National Cash Register 11-EN electro-mechanical adding machine from the early 1950s.