Let me say, I should have prefaced maybe with, "in a perfect world". I know most wrist worn GPS devices will report long but as a result of "post-processed" data. Where there is multi-path, like urban canyon environment( city marathons) it's a crapshoot. Distance can be way long or intolerably short depending on severity. Even the marketplace's hands down favorites have produced bad runs when worn on the same wrist in the same workout against "inferior" product. When our team measures for distance accuracy, the course has to be traversed exactly as measured by wheel or GPS, otherwise the GPS is doing its job and reporting distance as it was traveled. Lots of variables to consider and manufacturers solve their issues differently depending on the expectations of the user. I'll try to be more "User-centric" than engineering in future posts. Love the comments and the information from runners and cyclist!!