Abstract: An athlete (1) measures sprint time by locating a smartphone (3) having a camera and crystal oscillator clock which is first activated at the finish line. The sprint end time is recorded by a photo stamp time app activated by a video trigger causing the smartphone (3) to send a RF stop event signal to the athlete's wrist mounted motion sensor (2). Before this a sensor timer or clock is started via the sprinter's start event. The sprinter's start activates the sensor's clock and saves the captured start time including time drift error. Upon the phone app selecting the run time function, a sync command sent to the sensor (2) by the app zeros out the phone and sensor timers. A one-time crystal calibration routine correcting for drift errors caused by the smartphone's operating system is activated which provides the sprint with a corrected start time.