I got an ELEMNT BOLT GPS unit for OTGG to better the odds when I get left behind and come to a fork. Went for my first ride with it yesterday. 102.6 miles. Sounds about right. The portions I have measured off my Thomas guide checked very closely.
But!!!! Altitudes and elevation climbed. I rode a basically flat route out to a reservoir in the foothills, around, then basically flat with several 1-200' hills and some rollers, then a 1100' climb over the Chehalems (with an elevation sign at the county line/divide).
I was well over 1000' of climbing before I even got to the reservoir. Approaching 4000 before I started the final climb. 5400' for the day! (My tabulations would have been flat to the lake, 700' around, say 400 to the base of the climb, 1100, then downhill and flat so 2200'.)
And the altitudes - at first I believed them and found it interesting to learn the elevations on known points. Then I started noticing odd discrepancies. OK, not perfect. Over the final climb I did not watch the progress but looked when I passed the sign. 1006'! I'm betting the county surveyors were in to within oh, say 20'. If that is the case, my GPS missed by around 266' More than the elevation of my house above sea level.
I am now quite aware that many of the numerous digits on this device are insignificant, including more than a few to the left of the decimal. And that ride total "elevation gained"? BS with capital letters. My ability to be impressed with others' claims to massive amounts of climbing just took a big hit.