Re: [RC] Accuracy of GPS  Sarah McIntoshre: math clarification..... 7% slope does not have a linear (1:1) relationship to vertical distance. to get the actual distance travelled (upon a slope), we have to use grade 11 physics. We don't have a scientific calculator on hand, so we just played around with a measuring stick, and a 7% slope gives about 1.4 % increase in distance of travel up slope. i.e. put a yard stick on the floor touching the wall at right angles. lift the wall end of the yard stick 6". This is a slope of about 7%, and you only increase distance by about 0.5" . 0.5"/36" is 1.4% The higher the percentage of slope, the more the increase of total distance. (expontial relationship) Use the same yard stick and measure up the wall 36", which is 45% slope. Now the distance is 51" total, an increase of 16", which is about 42% more distance than flat. You can see from these two examples that the relationship is not linear, and 7% slope does not = 7% increase in distance. Sarah McIntosh p.s. don't forget, 7% slope = 8.1 gradient = 12.3% grade  these are all different methods of measuring vertical rise over horizontal distance. sometimes these distance calcs. are confusing, as people interchange some of these terms, without understanding they have different meanings. <snip> Tevis, the grandmother of all "hilly courses" (with a total of ~40,000 of elevation change...22,000 down and 18,000 up in 100 miles) has an average grade of about 7%...so, if you GPSed Tevis, and the GPS had perfect acquisition at every turn in the trail (unlikely) and the Tevis trail actually is exactly 100 miles (also unlikely), then the GPS would tell you that you had gone about 93 miles because it wouldn't take into account the average slope of ~7%. <snip> =================================== Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! ===================================
