Tasco Pocket Arithmometer - Slide Adder
Tasco Pocket Airthmometer, circa 1945
Tasco took over production in the early 1940s, and their adder has a chrome finish as shown. Earlier, in the 30s, this same design was being sold as the Gray Pocket Arithmometer and had a dull gray nickel finish . The Gray design in turn seems to be based on the even earlier German Trick Slide Adder.
The metal 'subtraction shield' or slide has been raised (see above) in order to perform subtraction.
The clearing lever is shown in the fully extended position (see above) in order to clear the result window with all zeroes.
The view of the back shows how the subtraction slide is attached.
JMGoldman has some nice pictures and an instruction manual at: