Garmin answer to GPS accuracy at slow speeds.
I have calculated grounds speeds vs ping rate (refresh position every 1 sec) of gps. It want work good at slow speeds. Here is why according to Garmin rep.
Dear Tom,
I was able to find this article at gpsinformation.net that will hopefully answer your questions regarding why one has to travel at least 2.5 miles/hr with a gps unit.
http://gpsinformation.net/main/gpsbearing.htm
Thank you for contacting Garmin.
Best Regards;
Bernardo R.
Product Support Specialists
Garmin International
1200 E. 151st Street
Olathe, KS 66062
1-800-800-1020
www.garmin.com
Fax 1-913-440-5488