Originally Posted by Anicius

I've run a Garmin 64sx for several years with a Cateye Strada, overkill perhaps. I try to correlate the distance readings between them by adjusting the Cateye wheel circumference setting. I load the Garmin tracks into BaseCamp and data from both into a spreadsheet. My assumption is that the GPS distance is usually a bit less than the Cateye distance, since GPS uses more widely-spaced breadcrumbs than the Cateye, which may cut corners more on sharp turns. A straight out-and-back track is most likely to be accurate. If the GPS signal goes weird, however, and it puts you on the other side of the river from where you are, or some such nonsense, the distance on the GPS can exceed the Cateye. Sometimes it does that anyway, for no reason apparent to me. I think of my collection of BaseCamp tracks as the functional equivalent of a personal diary, and the distance correlation as a challenging puzzle.