I only said heart rate and 'effort' could be done by feel. For distance, time and height gain/loss I bow to technology

I 'feel' there are several reasons why the Green appears to be a different height before and after the ride on the Garmin.

1. the Garmin has no true feelings

2. Andrew took a lot of air on the ride, which confused Garmin.

3. Garmin was so pissed off at listening to the girls' jam recipes and knitting patterns during the ride, it decided to give bum info.

4. The Green must be lower at the start of the ride with the weight of so many riders on it at once, but they return in dribs and drabs.

I'm sure there are many more equally plausible explanations.....