Exactus adder

Exactus stylus-operated adding and subtracting device, 1955-1965.
Exactus stylus-operated adding and subtracting device, with swivelling half plate for add and subtract options, marked "Mini-Add Made in England", c. 1950. The Exactus is one of several simple stylus-operated calculators to have been popular in the mid 20th century.
 
Currently on display in:
Mathematics
Year made :
1945-1955
Inventory number :
1981-861