It occurred to me you might want to get the GPS coordinates from your GPS and plot it on the map. There is an easier way. Mark the trailhead as a waypoint when you start. Then measure a bearing and distance from the trailhead. Of course, you will have to orient your map properly and be sure you know if you are using a true bearing or magnetic bearing on the GPS. You will need a good compass for this. Usually, there is only one distance on the trail that will make sense even if you aren't accurate on the bearing.