wrhobson

Hello to everyone. I am working on a hobby project and have been using several GPS USB "dongles" and exploring how they behave when interfaced to a PC program. I have noticed some puzzling behavior when watching the TRACK information presented once per second in the RMC sentence. Does anyone know if the TRACK field in the RMC sentence is dependant on any particular speed being acheived by the GPS unit? It seems that at slow speeds (like walking pace) the TRACK field is all over the ballpark (like it can vary 40-50 degrees from the actual path eing traveled) while, when in a moving car, it tends to stabilize (although it still isn't as stable as one would expect when moving down an apparently absolutely straight road). Am I misunderstanding what I should expect from these units? Thanks for any guidance you can provide.