tome
New member
Actual Timing
As promised, some data to show GPS time variation. This was recorded an hour ago on my Garmin 76 handheld. It's calibrated against an absolute time standard and shows 900 successive samples.
This GPS set outputs time in various messages at a 2 second interval, and the graph shows the error if you were to assume the time in the message was actual time. The graph shows 30 minutes of data using the GGA sentence, and the variation is approx 0.25 second (~0.1s 2 sigma). During the period, there were 26 constellation changes and the number of SVs varied between 6 and 8 (there are some obstructions around me).
Hope this puts to bed the myth that you cannot use GPS time for sight reduction, though I'd repeat the earlier point that it's safer to use it to rate your chronometers in case of GPS/power failure.
<hr width=100% size=1>
As promised, some data to show GPS time variation. This was recorded an hour ago on my Garmin 76 handheld. It's calibrated against an absolute time standard and shows 900 successive samples.
This GPS set outputs time in various messages at a 2 second interval, and the graph shows the error if you were to assume the time in the message was actual time. The graph shows 30 minutes of data using the GGA sentence, and the variation is approx 0.25 second (~0.1s 2 sigma). During the period, there were 26 constellation changes and the number of SVs varied between 6 and 8 (there are some obstructions around me).
Hope this puts to bed the myth that you cannot use GPS time for sight reduction, though I'd repeat the earlier point that it's safer to use it to rate your chronometers in case of GPS/power failure.
<hr width=100% size=1>