How do I activate and deactivate the Child Lock on the WD-1016(0~9)S?

Child Lock is activated by pressing and holding the Option and Temp buttons simultaneously. To deactivate it, press the Option and Temp buttons simultaneously again. When Child Lock is set, all buttons are inoperable except the power button, and the Child Lock symbol is shown on the display. Child Lock is automatically canceled when operational errors occur and also works when the power is off.