GoolRC LCD Digital Pitch Gauge For Align TREX 150-700 Flybarless Helicopter On/Off button allows you to conserve battery life. Hold button will stop the sensor from updating the angle that it senses. Useful for those who are working in an unstable environment. Zero button allows you to set "0" at any given position of the sensor.. This allows you to see your pitch travel at any interval. Battery TypeCR2032 Without battery(it's not safty by air mail)