Best way is to mark a waypoint. Turn on the range rings. get within casting distance of your waypoint and see how it matches up with the range rings. I can usually cast the distance to the second ring on my unit. Also turn on the heading indicator. You can accurately cast to a waypoint every time with those two things on.
When range rings is "ON" and going to a waypoint, look in the lower right hand corner of your unit. There will be a number showing the distance between each ring. If you zoom in or zoom out the number(or distance between rings) will change.