This evening I'm cleaning, repairing and refurbishing a Comptometer model 3D11 from the 1950s. This was the last Comptometer the company made and has its final speed and accuracy improvements before the world moved to electronic calculators.
@kyle Neat. Where or how is the sum displayed?
@sbeebe The register is in the front of the device lined up with each column of keys. In the picture everything is currently blank but once you depress a key it would add to the corresponding register. I demo a similar (but a few decades older) Comptometer in this thread.
https://social.librem.one/@kyle/107113386138173691
Once I finish cleaning and repairing this one I'll follow up with a thread demoing and explaining it.
@sbeebe Yes I would say that Comptometer and the Curta are great examples of peak mechanical calculators, with a Marchant Silent Speed being another if you include electrically-driven ones.
@kyle Fantastic! Thank you for sharing. What a cool machine. It seems like they are peak mechanical prowess.