You do realise I've done an extra lap in at least two of those Hillingdon '10's? You don't need to take a wrong turn to look like an idiot :)
I've done that.
Now I have my Garmin and check the distance.
One time I forgot I had left it on km instead of miles and, after about four laps I checked it and thought I was going really fast and had got into the zone where I'd done a couple of laps without realising it...
After sprinting for the wrong finish in the Hounslow 100 one year I generally swap my Garmin to Imperial for the distance TTs these days to avoid confusion maths.
I remember that, the gezzers with the picnic table a few hundred yards short!
I always mean to swap mine but it is another thing to forget. Like zero-offsetting my power meter, which I didn't do last night, so power data is garbage.
I've done that.
Now I have my Garmin and check the distance.
One time I forgot I had left it on km instead of miles and, after about four laps I checked it and thought I was going really fast and had got into the zone where I'd done a couple of laps without realising it...