Hands-free lap timing with your phone's GPS: choose the circuit and layout, press Go in the pits, and drive.
You can time laps without an account. Log in to save them to your garage and compare with other drivers.
Tap the map at each side of the track where the start/finish line is. Or skip this and tap Mark line as you cross it.
Choose a circuit to see the map.
Press Go in the pits, mount the phone with the screen facing you, and drive. Trackism starts timing at the line, keeps going lap after lap, pauses when you stop in the pits and picks up again on your next run. Hold Finish when you're done for the day. The screen stays on while timing: browsers can't use GPS with the screen off.
Phone GPS updates about once a second; Trackism works out the moment you cross the line between updates, so laps are usually accurate to around two tenths. A dedicated GPS receiver will be more precise.