HP -225 Owner's Manual page 154

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 usually remains intact.
To reset the calculator, hold down the key and press [LN]. If you
are unable to reset the calculator, try installing fresh batteries. If the
calculator cannot be reset, or if it still fails to operate properly, you
should attempt to clear memory using the procedure described in the
next section.
Clearing Memory
If the calculator fails to respond to keystrokes, and you are unable to
restore operation by resetting it or changing the batteries, do the fol-
lowing procedure. These keystrokes clear user memory (like [CLEAR]
{ALL} ), and may be possible when the keyboard is not functioning
properly:
1. Press and hold down the key.
2. Press and hold down [z].
3. Press [Z+]. (You will be pressing three keys simultaneously.)
The HP-22S displays MEMORY CLERAR if the operation is successful,
and these start-up conditions are set: period decimal point, FIX 4 dis-
play modes, decimal base, and Degrees mode.
Memory may inadvertently be cleared if the calculator is dropped or if
power is interrupted.
146 A: Assistance, Batteries, Memory, and Service