Kyle Rankin @kyle@librem.one

To zero things out, you pull on a lever at the top. Basic tallying, like scrabble scores, can be done pretty quickly on one of these after some practice. You can also do multiplication via repeated addition and left shifts like with other adding machines.

To subtract, you slide a panel from the bottom upwards, which aligns new numbers with the holes. Now you slide up instead of down, unless you need to carry a one, in which case you slide down around the hook. I'm not a fan of this part of the design--it is pretty cumbersome.

As you slide rows down you notice some numbers in a row are colored red. That signals that when you add those numbers, instead of sliding down, you slide up and around the "shepherd's hook" to carry the one. Here I added 5.

This is a Tasco Pocket Arithometer. It was probably made in the 1940s but is based off of older Arithometer designs. It is sized to fit easily into a shirt or coat pocket. To add numbers you place a stylus in the appropriate row and drag down, which adds to the existing total.

Today's other antique find is this pair of mechanical pocket calculators. Both came with their original case but sadly neither had their stylus.

Each pocket calculator in my collection has a slightly different way of performing arithmetic, probably due to patents.

Today's antique finds: a Gillette red tip and a Slim adjustable. The red tip came with a wooden case which I don't think is original--my understanding is these originally came in a plastic case.

Well this is disappointing. While trying to loosen up stuck mechanisms a few teeth broke off of an important gear. Guess this is now a parts machine.

I don't dispute that jails are hard to break into, but they are even harder to break out of. How many of us would choose to live in a prison in real life? Instead we make risk assessments that balance personal freedom and security, and the digital world should be no different.

The security industry has largely failed to build security measures without reducing a user's freedom more than attackers. It's not only harder to build security solutions that give users control, it reduces dependence on the vendor. This is why vendors just build jails.

It's pretty complicated all right...

This is a Marchant "Silent Speed" ACR8D electromechanical calculator from the 1940s. It is currently jammed up, stuck on a division problem it never finished, and is apparently the most complicated mechanical calculator out there. Wish me luck!

To close out this thread, here is correspondence between Felt himself (the inventor of the Comptometer) and Zenith Pub. Co.

Even though I have more "advanced" mechanical calculators like my Monroes, the more I use this Comptometer the more impressed I am at the design. It's actually faster to use than my Monroes, at least for addition and multiplication.

Experts would only use the bottom rows so their hand was stationary. To enter larger numbers they'd enter two smaller numbers so to enter an 8 they'd enter 4 two times. This and later models had features to catch "fat finger" errors and partially-depressed rows.

Division was possible via repeated subtraction starting from the left and shifting to the right. There were no underflow bells, you'd just have to know when to stop subtracting a row. This is hard to do one-handed so I didn't film a video of that.

Subtraction was weird. You'd subtract w/ addition by the complements method, but would first subtract one from the number, then press down that number using the small digits on each key. You also slide the correct metal tab at the bottom to stop the carry. Here's 9 - 2.

You can perform many calculations surprisingly quickly and w/ one-hand. A well-trained Comptometer user was probably as fast as you'd get until electromechanical calculators. Here I'm calculating 1024 x 768, which just requires pressing 768 a few times and shifting left.

The Comptometer had a superior design. Pressing a key immediately updated the register, no need to pull a lever (the lever here clears the register). This design was so effective it stayed essentially the same (with minor improvements on error prevention) through the `50s.

This is a Comptometer Model E mechanical calculator, made between 1913 and 1914. Comptometers were made starting around 1900 and were a direct competitor to the 1908 Burroughs adding machine I featured earlier.

I didn't realize just how much I blamed Microsoft for the current state of passwords until I sat down to write about their "passwordless future": https://puri.sm/posts/microsoft-ruined-passwords-now-aims-for-a-passwordless-future/