I am very new to geocaching, but I have already noticed anomalies in GPS readings specific to the brand/model used. Why not provide a box for GPS brand/model used to mark a cache site on each cache page? This would give those of us who own both Garmin and Magellan units an opportunity to adjust accordingly when seeking extremely precise coordinates.
I fully recognize that GPS performance can be greatly affected by a multitude of factors (weather, satellite position, WAAS acquisition, etc), but I would bet that many GPS users have noticed brand/model consistencies when comparing GPS readings.
