Garmins can indeed be wrong, but if your entire perception of distance is based upon what your Garmin has always told you, especially when training for your marathon (!), then if it says you're half a mile further on than you should be, then your mind and legs will probably believe it, just as they have for the last 16 weeks of a training schedule. That's a very long sentence ... (half a mile too long?)
Well considering the re routing they had to do and the loops we had to do 3 times, I thought that was great! Hylands park was particularly pretty (sunshine helped), and the crowd support was excellent. Gold stars to the marshals and to whoever thought of handing out bananas and jelly babies. And I did manage a PB 4.56.23, nearly a half hour improvement on my 1st effort. my garmin measured the course at 26.62 miles. A day on my sofa today!
As far as I'm concerned weather on the day is almost perfect (a bit hot) but sooo much better than last time (5 hour monsoon). And as I don't know Chelmsford at all, wherever they route it will be interesting. Looking forward to staggering round any bit of park they fancy!