quote from manual
on the bottom of the computer unit, to the upper right of the battery door is a small hidden RESET key. Pressing this key with a toothpick or other small pointed object will reset all programmed values to their default values and resets the microprocessor. This may also be accomplished by removing and reinstalling the units' battery.
CAUTION - pressing the RESET key will automatically clear any information from the units' memory
HTH baz