Discrepancy between GPS odo and track log readings
 

Greetings all, has anyone ever noticed a discrepancy between the trip odometer display reading on your GPS (mine, a Garmin 76CSx) and the actual cumulative distances recorded by the GPS track log - like below:

You would think they would be identical but I am coming across an odo reading sometimes 20% over which puts a spanner in my works. I have yet to take it out for a measured run. My instinct is to trust the track log readings.

thanks

Chris S

This is normal.

The tracklog converts your route to a number of straight legs. It uses the length of the straight legs to calculate “the actual cumulative distances recorded by the GPS track log”.
A route based on straight legs will always be shorter then the route you drive

To reduce the error you have to set up the GPS so it adds points often to the tracklog but this will limit the length of the log.

If you drive in a straight line it will work…

Edit: Like this:
http://www.actiontouring.com/pic/GPSroute.jpg

Thanks for the quick answer. I guess that explains it.
I see it is set on 'Normal', recording every 5-230 metres and every 1-15 seconds.
I'm surprised there was such a discrepancy but maybe going slowly on bendy tracks accounts for it. So the odo gives the true distance.

Ch

On my 60Cx I've set the track log to 'auto - most detailed' or something like that ... that makes a typical day ride about 0.3Mb .. and it is set to save the track log to the memory card .. 2Gb ... there is a lot of 'free' space on the card so running out of memory on it is not a worry. This improves the detail of your track logs ... make maps made from them much more useable .. and you can see enought detail to added in POIs afterwards .. like where you slowed to look at a view .. POI 'scenic area' etc.. I'd sugest you do the same Oh - and turn off 'lock on road' means the track log does not follow any loaded map roads... you don't want to copy their data (get your actual track - usually much more acurate than the map).