I have a Garmin Forerunner 301 which has served me well for 10 years. However I have noticed that my 1 km lap splits seemed very inconsistent when I felt I was running about the same pace. Problem came to a head this morning on a 13km run, where my splits were between 5.23 and 5.56 mins per km, except for one which was 15.13 mins/km. I exported the file as a TCX and opened the file in firstobject HTML viewer. The distances for each 1 km split varied from 0.9959km to 1.06km and one way out there at 2.726km. I had a look back into previous runs and find variations in the 1km split from 0.89 km with the worst being today's 2.726km. Funnily enough the summary on the "Lap" screen matches the total distance on the TCX file, but the individual lap lines add up to 1.7 km less. Makes you wonder how this thing is calculating the displayed data.
