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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:

FeatureValue
TypeArithmetic
Functions5
Keys20
Precision8
LogicAlgebraic
Display typeDischarge
Length133mm
Width81mm
Power Source4xAA sealed
Year introduced1973
Year discontinued1973

Replacements:

If you have a Keystone 390 that is no longer working, you can first try replacing the 4xAA sealed batteries. If that doesn't solve the problem, then you can consider replacing the calculator with a modern equivalent. We suggest the following current models as possible replacements:

See other calculators by Keystone