Blimey, that sounds complicated! Most of the calcs you do will be of TIME, I think, as the Planex seem to give you distance and speed; eg. you can travel at 3 km/hr over some sort of rough terrain and have 8km to travel.
Try learning how long it takes to go 1km (or mile) at given speeds;
eg. at 5 Km/hr it takes 12 min to travel 1 Km, so 7 Km would take 7x12 min = 84 min
at 15 Km/hr it takes 4 min to travel 1 Km, so 11 Km would take 11x4 min = 44 min and so on!
Make a table of most likely speeds; 2,3,4,5,6,10,12,15,20,30,60 Km/hr and corresponding times for 1 Km and get someone to keep firing them at you once you have learned them!