Garmin GPSMAP60CSx and Mapsource differ on routing?

[PloddinPedro]

I have just bought a GPSMAP60CSx and City Navigator Europe v9. I have used it for the first time today on a cycle ride. The mapping software produced a route from a series of waypoints which appears correctly on the PC screen at home but when downloaded into the GPSMAP60CSx the route at one point diverts around a longer loop and follows a different path to that shown on my home PC screen despite all the waypoints loading correctly. This means that I apparently cannot rely on the handheld to follow a route plotted in City Navigator. I understand that the download to the GPS comprises only the waypoints and that the GPS unit re-calculates its own best route, but I had all the relevant preferences - use bike, follow road, shortest route, etc. - set the same in both mapping software and the GPS unit so why did the latter come up with a different route? Any ideas?

[mikealder]

Check your units of position it is possible they are set to use different reference grids, look for:

NAD27
WGS84
British National Grid
Lat/ Long

Make sure they are set to use the same as the system your trail was created under - Mike

[Frabble]

Even though they use the same map data, there may be differences between a route calculated by MapSource and your GPS unit. You don't have exactly the same options for both, for example MapSource has a Road Selection Option which I've discovered will give a different route for even a minor change and your 60CSx has a Calculation Method option which presumably sets how "deep" the routing is performed.

Only thing I can think to do is try and find out why the longer loop was taken by the unit and maybe inserting a via Waypoint so that it calculates the same route as MapSource.