Canon P20-DX User Manual page 6

When printing is not required (i.e. the printer switch is OFF), the calculator can be
used as an ordinary display model.
Input Buffer Register Function: The buffer register allows all numbers, basic
function and other function keys to be depressed while numbers are being printed.
The calculator remembers up to 9 key entries in the register, and calculates them
in the sequence entered.
Automatic Power Off Function: When the power switch is turned ON but none
of the keys is depressed for more than about six minutes, the display goes out
automatically.
In this case, depress the "Power On/Paper Feed" key to start the calculation,
0 will appear on the display.
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