Addometer calculator
Built from 1928 to 1960s
This is a mechanical adding calculator, the Addometer model B.
It seems a big and heavy ruler, in inches. There are some numbered wheels, and you select the number with the stylus. Using it is very simple, you can do additions, subractions and multiplications.
It's also portable.
Here there is a video, you can see here how it works.
