The driver is using a « trick »

Setting mutiple tracks for the mass-start of a cross-country skiing competition.
The Alpina F-250 snowgroomer is equipped with twin track-setter, both with Vibra-cut system.
The driver is using a « trick » to keep the tracks parallel and equidistant at each of the passes: he has installed a « ruler » with a fluorescent tip in the front of his Sherpa, and he drives while keeping the ruler tip over the previous track.