Replacing the battery
Step 1: turn the power off with 
and 
. The backup battery is an LR44 button cell, 1.5 volts. Turn the calculator face down. Remove the screw on the back with a small screwdriver. Lift off the battery cover. Pry the old battery out with a pencil or a pen tip; never use anything sharp. The old battery is out. Insert the new battery with the plus side facing up, and close the cover. Finally, press the 
switch on the front with a pen tip: the display shows 0. and DEG. If not, take the battery out, put it back, and check again.
1 The backup battery is an LR44 button cell 
2 Turn the calculator face down 
3 Remove the screw on the back 
4 Lift off the battery cover 
5 Pry the old battery out with a pencil 
6 The old battery is out -
7 Insert the new battery, plus side up, and close the cover