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:
|Power Source||4xAA sealed|
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: