Receiver WAAS On and Off, 30-Minute Tests in the Open, Night and Day
(Red indicates WAAS On)

Summary:

                        WAAS  95% ERROR DRIFT/min  AVG.ERROR*   END TIME  RUN TIME  AVG.ALT.ERROR*#
*Error after averaging in 2-D   #Based on a newly surveyed altitude of 314m

(Night/Evening Tests, NAD-83 Reference Coordinates)

 Vista 2.15        on     2.1m      3m      0.9m@306°    10:33pm    30 min.     -6m
 Vista 2.15        off    1.8m      2m      0.7m@352°    11:08pm    30 min.     -8m
 G-76 Map 2.04     on     1.8m      2m      0.8m@292°     7:05pm    30 min       0m
 G-76 Map 2.04     off    1.9m      2m      0.7m@292°     6:24pm    30 min      +1m
 Magellan M-330    n/a    2.0m      1m*     1.0m@267°    10:33pm    1 hr.       -2m

(Day Tests NAD-83 Reference Coordinates)

 Vista 2.15        on     5.8m      3m      3.4m@282°    11:21am    30 min.     -2m
 Vista 2.15        off    7.6m      3m      5.1m@309°    11:59am    30 min.     -2m
 Magellan M-330    n/a    8.4m      0m*     7.0m@001°    12:30pm    30 min.     -1m
 Magellan 330 WAAS on     2.5m      1m*     2.0m@273°    10:36am    30 min.      0m
* Due to automatic averaging

Observations:
    GPS accuracy is generally better at night when the ionospheric errors are less.
    WAAS ionospheric corrections are therefore less apparent at night.
    The reference-point accuracy is confirmed with the average night error of 0.8m.
    This (and other) tests indicates non-corrected GPS units have a northward error bias.

    NOTE: The WAAS (WGS-84 datum) receivers have a nighttime north-westward bias of about
    1m as compared to the reference point which was established with DGPS (NAD-83 datum).
    In the Atlanta area, WGS-84 coordinates are 0.86m@329° from NAD-83 coordinates.
    Those that would like to measure this offset at their loaction can run HTDP.EXE or
    the interactive version (HERE).

Survey: USInfrastructure, Inc. later confirmed that the original DGPS averaging in the NAD-83 datum was accurate to within 0.05" of Lat/Long.

Night/Evening Tests

Vista WAAS ON, 95% Errors=2.1m


Vista WAAS OFF, 95% Errors =1.8m


G-76 Map WAAS On, 95%=1.8m


G-76 Map WAAS Off, 95%=1.9m


Magellan M-330, 95% Errors=2.0m

Day Tests

Vista WAAS ON, 95% Errors=5.8m


Vista WAAS OFF, 95% Errors=7.6m


Magellan M-330, 95% Errors=8.40m


Magellan M-330 with WAAS, 95%=2.5m