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Casio fx-991ES (Natural Display)

Casio fx-991ES
Image: Wikimedia CC BY-SA 3.0

The Casio fx-991ES is a scientific calculator with 8 digits precision and formula input logic. It has 403 functions, 50 keys, and an LCD (liquid crystal) display. The power source is Solar. The calculator was manufactured in China. Note: Functionally the same as fx-570ES with solar power

Facts at a glance:

FeatureValue
TypeScientific
Functions403
Keys50
Precision8
LogicFormula
Display typeLCD
Length161mm
Width80mm
Thickness12mm
Weight105g
Power SourceSolar
CountryChina
Year introduced2005

User Manual

You can download the Casio fx-991ES manual from this external link.

Diagnostics

Note that diagnostic tests generally delete any data on the calculator. Be sure to back up any important information held in the calculator before running these tests.

While holding SHIFT and 7 keys (or just SHIFT key for early models) press the ON key. Pressing the SHIFT key shows 5 display test patterns in turn, followed by the ROM version. Press AC to get the contrast test screen, and press AC again to get to the keypad test - the numbers then increase as each key is pressed in the correct order (omitting the ON key which exits test mode).

Replacements:

If you have a Casio fx-991ES that is no longer working, you can consider replacing the calculator with a modern equivalent. We suggest the following current model as a replacement:

See other calculators by Casio