Kyle Rankin @kyle@librem.one

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.

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.

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.

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.

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.

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.

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 server's anti-virus wasn't up to date... https://arstechnica.com/information-technology/2021/10/passengers-couldnt-fly-after-nhs-vaccine-passport-went-offline/

Eventually John Conner will drop from the future into that street. That much is known, the machines just don't know exactly when. https://sanfrancisco.cbslocal.com/2021/10/14/dead-end-sf-street-plagued-with-confused-waymo-cars-trying-to-turn-around-every-5-minutes/

We are testing out a new experimental feature in PureBoot to extend tamper detection past /boot into the root disk. I write about the feature and my thought process behind developing it here: https://puri.sm/posts/new-pureboot-feature-scanning-root-for-tampering/

"I'm really into mechanical calculators and also security. A mechanical cipher machine would be really cool to add to the collection." Then I saw the going rates for vintage WWII cipher machines... #nope #toorichformyblood

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.

There are few things as satisfying as fixing something you are unfamiliar with by researching how it works and applying basic troubleshooting skills. In other news, the furnace works again (insufficent pilot light flame around the thermocouple).

Adding to my collection...

Due to the size and the case design, I suspect Addometers were mostly stored on or in desks and pulled out for quick arithmetic and they work well for that. The Imperial model I have was probably thrown in a toolbox and has lots of wear and even initials carved in it.

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.

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.

To multiply, perform repeated addition and shift left for each term in the multiplier. Here is 12 x 12.