HP HP-20S - Resetting the Calculator

6. Slide the tab of the battery-compartment door into the slot in the
calculator case.
Now turn the calculator back on. If it does not function, check that
the orientation of the batteries is correct. If the calculator still does not
function, you might have taken too long to change the batteries or
inadvertently turned the calculator on while the batteries were out.
Remove the batteries again and lightly press a coin against both battery
contacts in the calculator for a few seconds. Put the batteries back in
and turn the calculator on. It should display ALL CLr.
Resetting the Calculator
If the calculator doesn’t respond to keystrokes or if it is otherwise be-
having unusually, you should attempt to reset it. Resetting the
calculator halts the current calculation and clears the display. Stored
data remains intact.
To reset the calculator, hold down the key and press at the
same time. It may be necessary to repeat the reset keystrokes several
times. If you are unable to reset the calculator, try installing fresh bat-
teries. If the calculator still fails to operate properly, you should
attempt to clear all of memory using the procedure described in the
next section.
Assistance, Batteries, Memory, and Service 113