Pacing is a skill that helps you judge the distance you need to travel to reach the control.
Every two paces on either your left or right foot is counted for 100m. This is then a base number from which you can work out 200m, 250m etc.
Of course, this will vary somewhat if you are climbing or going down hill. Uphill shortens the pace and therefore more paces needed. Equally, going downhill you may well lengthen your pace counting slightly less
It will help you to know if you have overshot the control too if you have counted too many paces, chances are you have gone past the control
Remember: Calculate the paces accurately, soon enough they will be second nature.