Its surprising how far from a mark you end up after deciding to drop anchor. If the tide is running hard you will have drifted a bit while the anchor is falling, then it will drag a bit before digging in, then you let out rope, probably 3 x depth of water. Then you fish, and the tide takes your bait even further back! Use the GPS track feature like ChrisP says, mark the point you want to target, let the boat drift, then steer to the mark noting the bearing. When you get to the mark, keep going on the smae baering for, say 150 metres then mark again and anchor. See where you end up relative to the first mark, if you are not on where you want to be then up anchor and drop again the same relative position from your first anchor mark as you were in error over your fishing mark. If you have done that carefully you will be spot on. Spend some time getting used to your GPS features if you haven't already, so you can do all that stuff without having to mess with the manual. Hope that helps. An easier way is to fish near other boats, you can generally work out tide and wind push by looking at them, and eyeball estimate where the anchor is relative to the boat by looking at the angle of the anchor rope.