Our product has unique electronic compression depth and frequency detector. 1. First right operation: the 4 indicate light on the left shoulder will be on. 2. the lights off: lack of battery or operation mistake 3. when start the operation, yellow and green light will be off 4. red light: Press frequency 0-60 beats/min Yellow light: Press frequency 60-80 beats/min Green light: Press frequency 80-100 beats/min 1)right operation: 2 green lights on Press frequency >100 beats/min 2)red light flashing:compression depth insufficient