Press and hold the "Cond/>" switch on the front panel for 2 seconds or more. This procedure makes the keys lock.
While the keys are locked, key operations are not accepted. If you perform a key operation in the key lock mode, "K.P." (Key Protect) is displayed at the bottom center of the display unit.
To unlock the keys, press and hold the "Cond/>" switch for 2 seconds or more again.