Wilsons Sandbox

> > calibrated the BC by taping off the distance between two chalk marks on >the >> concrete, equivalent to two revolutions of the front tire. This total >> distance was approximately 82.9 inches, and I figure I couldn't measure it >> accurately to nearer than an eighth of an inch, for a relative error of >1.5 > > percent.

Hi Dreas, Your tire will increase somewhat in diameter at speed, which reduces the number shown on the BC. If the radius increases by 491/485 (=.16") then there you are! .16" increase seems very likely. Even so, I'm quite suprised the two numbers are as close as they are! Tom -- +------------------------------------+ | CycoActive Products tel (206) 323-2349 | 701 34th Ave fax (206) 325-6016 | Seattle, WA 98122 USA | website: http://www.cycoactive.com | e-mail: TomMyers@... +------------------------------------+

> On the other had, if the GPS has a negligible error, the accuracy of the

BC

> is 20% better than I expected, or pretty good (I think) for a relatively > crude calibration procedure. > > So to really figure out what's up, I need 99 others of you out there to do > the same comparison, and then we can see if the relative accuracy I found > really was a two-sigma event. Get riding! > > Dreas

I dont think the GPS is as accurate when their is alot of up and down hill riding. It works great on flat surfaces. If the BC is calibrated right, then it is probably more accurate. As long as you keep the front wheel on the ground. MotorMark

> --- In DSN_klr650@egroups.com, "Dreas Nielsen" wrote:

> > > > I don't know the relative precision of the GPS's distance > > measurements (neither the Garmin manual nor Web site provides this > > information) (and it's probably speed-dependent), but I'd be > > surprised if it was much better than a couple of percent. > > > > Dreas >

> Garmin specifies the speed of the GPSIII(and +) at 0.1 knot, pretty darn > good. The errors in the GPS come from the fact that most of the units we

use update

> once per second, and compute speed in terms of the straight line between

the

> two points, even though in a turn you travel a larger distance. > > Steve A.

An error of 0.1 knot (or 0.11 mph) at 58 mph, the average rolling speed I made on my trip, is equivalent to 1.9 percent, which I certainly consider to be not much better than a couple of percent. I don't mean to argue that that is not pretty darn good, but that it indicates that the correspondence between the BC and GPS was markedly better than expected. Dreas

> -----Original Message----- > From: Mark Wilson [mailto:motormark@...] > > > On the other had, if the GPS has a negligible error, the accuracy of the > BC > > is 20% better than I expected, or pretty good (I think) for a relatively > > crude calibration procedure. > > > > So to really figure out what's up, I need 99 others of you out > there to do > > the same comparison, and then we can see if the relative > accuracy I found > > really was a two-sigma event. Get riding! > > > > Dreas > > I dont think the GPS is as accurate when their is alot of up and down hill > riding. It works great on flat surfaces. If the BC is calibrated > right, then > it is probably more accurate. As long as you keep the front wheel on the > ground. > > MotorMark >

The GPS can measure your elevation, and elevation difference, so it could measure the 3D, rather than 2D, displacement between two successive positions. Dreas

> > The GPS can measure your elevation, and elevation difference, so it could > measure the 3D, rather than 2D, displacement between two successive > positions. > > Dreas >

I dont know about your GPS, but with mine, I can sit still, and look at my GPS altitude reading, and it is telling me I'm at 700 ft one minute, and 850 the next, even though I havent moved one inch. MotorMark

A lot of GPS units (perhaps most) are notoriously unreliable for altitude readings. Usually you have to let it sit in one spot for 10-15 minutes to even halfway believe the altitude reading. -----Original Message----- From: Mark Wilson [mailto:motormark@...] Sent: Tuesday, August 01, 2000 11:31 AM To: KLR650 List Subject: Re: [DSN_klr650] NKLR: GPS vs bicycle computer mileage

> > The GPS can measure your elevation, and elevation difference, so it could > measure the 3D, rather than 2D, displacement between two successive > positions. > > Dreas >

I dont know about your GPS, but with mine, I can sit still, and look at my GPS altitude reading, and it is telling me I'm at 700 ft one minute, and 850 the next, even though I havent moved one inch. MotorMark Visit the KLR650 archives at http://www.listquest.com/lq/search.html?ln=klr650 Support Dual Sport News... dsneditor@... Let's keep this list SPAM free! Visit our site at http://www.egroups.com/group/DSN_klr650 To unsubscribe from this group, send an email to: DSN_klr650-unsubscribe@egroups.com