Canon P20-DX User Manual page 13

2, When dividing by "0".
3. Buffer Register Overflow
When the sequential operation is made using more than 9 keys; depress the "CE"
key or the "C" key to clear the overflow.
4. If the batteries are weak, the "CE" or "C" key may not unlock the keyboard. In
this case, change all four batteries at the same time, or use the AC Adapter
AD-11.
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