Keystone 390
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 |
| Year discontinued | 1973 |
Replacements:
If you have a Keystone 390 that is no longer working, you can first try replacing the 4xAA sealed. 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: