How to know the robot is miss-tracked or not in Adventure Race and Treasure Hunt???

A lot of students keep asking how to judge the robot miss-tracked.

Miss-track means all wheels of the robot are on one side of the track line, so if any wheel still on the track line even it touch a bit track line only, the robot still haven't miss-tracked.

Only the wheels that use to support or move the robot is counted, the wheels that useless or just for decorate is not count, so don't put many wheels on the robot to avoid miss-tracked.