Antique Mechanical Calculator 

TIM ("Time is Money") - made from 1907 to 1940

This particular one is Model III, made some time before 1924. 

This model is on display in the National Museum of American History of the Smithsonian Institution. It is a stepped drum calculator based on the Thomas Arithmometer and was made by Ludwig Spitz & Co. in Germany, sold by the TIM Calculating Machine Co in Chicago.

It comes with a metal cover, which is very rare. It is massive - 27 lbs. Works well, the first register lever is a little tight but moves ok. Both the addition and subtraction works, the crank turns very smoothly. The zeroing levers work as well - except, again, for the rightmost one which snags a bit.

The two zeroing sliders work as well.

It is an amazing piece of early mechanical calculating history.