My personal experience with Garmin, Lowrance, Delorme and Humminbird is that none are as accurate as you would think them to be. Turn your unit on in the driveway, and I'd bet you see your position changing as you sit stationary. There's just to many variables to put you dead on. Take the built in error, then compound that with approaching the waypoint from a different direction, plus the delay of the brushpile showing up on the sonar, and finally the location of the GPS antenna in relation to the transducer. I've found my accuracy getting back to a waypoint improves considerably if I track back in the same direction I marked the W/P originally. Approaching at 90 degrees usually has me missing the brushpile unless it's a huge one.
