kBefore assuming malfunction of the calculator...
Perform the following steps whenever an error occurs during a calculation or when calculation results are not what you expected. If one step does not correct the problem, move on to the next step.
Note that you should make separate copies of important data before performing these steps.
(1)Check the calculation expression to make sure that it does not contain any errors.
(2)Make sure that you are using the correct mode for the type of calculation you are trying to perform.
(3)If the above steps do not correct your problem, press the Okey. This will cause the calculator to perform a routine that checks whether calculation functions are operating correctly. If the calculator discovers any abnormality, it automatically initializes the calculation mode and clears memory contents. For details about initialized settings, see “Initializing the Calculation Mode and Other Settings” under “Calculation Modes and Calculator Setup”.
(4)Initialize all modes and settings by performing the following operation: 19(CLR) 1(Setup) =(Yes).
Reference
kPower Requirements and Battery Replacement
Your calculator uses a TWO WAY POWER system that combines a solar cell with G13 type button battery (LR44).
Normally, calculators equipped with a solar cell alone can operate only when relatively bright light is present. The TWO WAY POWER system, however, lets you continue to use the calculator as long as there is enough light to read the display.
Replacing the Battery
Dim display figures when available lighting is dim or failure of anything to appear on the display immediately when you turn on the calculator indicates that button battery power is low. Note that you will not be able to use the calculator if its button battery is dead. When any of these symptoms occur, replace the button battery.
Even if the calculator is operating normally, replace the battery at least once every three years.
Important!
•Removing the button battery from the calculator causes independent memory contents and values assigned to variables to be cleared.