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

                  WAAS °95% ERROR ° DRIFT/min ° AVG.ERROR* ° END TIME ° RUN TIME ° AVG.ALT.ERROR*#
                                            (Day Tests)
 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

                                           (Night Tests)
 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

*Error after averaging in 2-D
#Based on a newly surveyed altitude of 314m
** Due to automatic averaging

    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.

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

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