Zero G measures the longest duration that the phone is in free fall (i.e. – zero gravity).
During a jump, there is a period of free fall during which the accelerometer detects no force. In order to achieve a maximum Zero G time, you can try holding the phone with a straight arm and jump up and down. Similarly, it is possible to keep the phone in a pocket, but it should not be too loose nor should you move your hips aggressively during the jump, as this will shorten your free fall time. Skydivers often experience up to 60 seconds of free fall.