I have now done 2 runs with my new Garmin and realise that I have been over estimating the distances I was running previously, although I have been running 30+ mins each time. My first run, which is my usual route, is only 4.6k and not 5.25k that I had worked out on map my run! it is a big difference. My longer run that I have done this morning was 5.25k and not 5.78k!!
I am very pleased with my new toy as it gives exact distances and times. It did tell me that I ran 5k in 32.32 mins.