a .500 tree means that the green light turns on exactly .5 seconds after last yellow light is activated. In other words if you get a .500 light, your ET is exactly how long it took you to pass the traps after the green light was lit. In this case a 10.00 with a .500 light takes 10.00 seconds to pass the traps after the green light, or 10.5 seconds after last yellow light was lit.