... operation:a) In stand-by state, short time press top right button (↑): Power display screen shows ... backfire welding, press this button a long time, only respond one time (X shows input value, same as follows ... welding, press this button a long time, and only respond one time.e) Stand-by state, digital show ... Err, press this button a long time, it only respond one time.h) Press each above button, buzzer ...