About movement in Pz8 rules, the distance is determined by the terrain that the unit is crossing.
For example a Medium Tank unit (in the Pz8 WW2 rules) moves 4" in open ground; let's assume it moves 2" than enters rough ground; it can move a further 1" (that counts as 2" in open ground).
Opposite example: the same unit starts in rough ground, moves 1" (that counts as 2" in open ground) then enters open ground, it can move a further 2".
Another example: a Medium Tank unit along a road, it moves 4" (that count as 2" in open ground) then exit the road, it can move a further 2" in open ground or 1" in rough ground.
At least this is how i play it