Keystone 390

Keystone 390
Image: Joe Haupt, CC BY-SA 2.0
The Keystone 390 is an arithmetic calculator with 8 digits precision and algebraic logic. It has 5 functions, 20 keys, and a gas discharge display. The power source is 4xAA sealed.

Facts at a glance:

Feature Value
Type: Arithmetic
Functions: 5
Keys: 20
Precision: 8
Logic: Algebraic
Display type: Discharge
Length: 133mm
Width: 81mm
Power Source: 4xAA sealed
Year introduced: 1973
YearDiscontinued: 1973

See other calculators by Keystone