My Garmin 60 consistently logs around +10% miles (over a 10-12 mile walk) relative to my Tracklogs digital mapping software and, more interestingly, a friend's GPS. So on returning lto the car last week we both set our logs going at the same time and measured against the car mileage. At 11 miles we were both within 0.1m of the car and each other! So why do I measure more on a walk? Is there a 3D effect (ups and downs) that computes differently on different makes of GPS?
