• Original Odhner Model 27

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My first calculator – the one that started the whole madness. I stumbled upon this one on the 12 July 2020 in the middle of the Covid-19 pandemic in a flea market.


A typical pinwheel mechanism with a stationary main wheel with 10 input digits. The output/counter sled has 13 output digits and 8 digits for multiplication/division. Resetting the output and counter is done individually by the cranks on each end of the sled. The buttons on the front are used to move the sled in steps but it can also be decoupled by the lever bellow them and moved freely. The inputs can be reset by the brass lever on the left.

The calculator also has a transfer mechanism which is activated by pressing the button on the right and then turning the reset crank one turn, resetting the output and transferring the result to the input.


Some external damage and a seized-up mechanism. Got it working after a (couple of) complete disassembly and thorough cleaning. Now works like a charm!