Garmin G-60C Accuracy as Compared to the Mgellan SporTrak Color -Under Moderate Tree Cover
NOTE: These tests are with static conditions.  For a dynamic test see (HERE)
Both units were run with WAAS On.  (Graphics by SA Watch)

                       95% accuracy           Average accuracy      Drift/Min
             G-60C        6.1m                    1.6m               16m
             ST-Color     2.6m                    1.2m                1m

Waypoint Averaging

There is also a manual way to determine accuracy of a marked and saved waypoint (which has been averaged for better accuracy.)  Garmin units have a waypoint averaging option, while Magellan units do 'automatic averaging' when not moving.

The below tests were about 5 minutes of simultaneous averaging (about the practical limit of someone trying refine a bearing and distance to a geocache).  The ST Color's automatic averaging was broken by rapid movement before averaging.  The Garmin waypoints were averaged, while the ST Color waypoint were just saved.

                       Error of Averaged Waypoint (distance in feet% and bearing)
WP test No.        Garmin C-60     @         SporTrak Color      @
   001#                 3.2'      51°              11.3'        27°
   002#                11.1'      43°               6.5'       309°
      007#                 5.2'     189°              10.1'       270°
      008#                 9.2'     160°              12.9'       129°

   003*                 5.1'                        2.7'
   004*                12.3'                        2.7'
   005*                 9.3'                        7.6'

# The test point is under moderate tree cover, and is about 1 m accurate.
* The test point is in the clear, and is about 5 cm accurate.
% As measured with G7ToWin by making the test points, the waypoint list "reference points".

The 60C "Measurement Count" remained at 0.  Upgrading to Ver. 3.10 fixes this.