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.