Aircraft turbulence is categorised as either light, moderate or severe. Air traffic controllers routinely ask pilots to report the level of turbulence that their aircraft is experiencing. These reports are called ride reports. Ride reports are used by other aircraft to decide which route and altitude to take to avoid the turbulence. Pilot assessment of turbulence levels are often subjective and inaccurate. The International Civil Aviation Organisation (ICAO) category definitions for turbulence are: 1.1g - 1.3g Light 1.3g - 1.5g Moderate 1.5g - Severe RideReporter uses the accelerometer on the iPhone to measure the turbulence level and gives the user a readout as to which category their aircraft is experiencing.