"gotbent" <
[email protected]> wrote
> 2% at ten miles is almost a quarter mile( a couple tenths BTW). That's
> about 2 miles in a century. Not so very accurate after all.
It's the same accuracy, of course, 98%. As "accurate" at 10 miles as at
100.
My point, perhaps not well made, was with a group of "non-compulsive
cyclometer calibrating cyclists", a difference of 2% is not unreasonable.
I've
seen much larger variations, but generally there's someone who just used the
calibration number from the cyclometer book....
Riding with a friend, our odometer readings are consistently within
a couple of tenths over 25-35 miles. That's a difference of less
than 1%.
> [98% accuraccy] Fine enough for me though. How about for you?
Except for a measured course, how would I know the difference? %^)
I don't consider myself obsessive about cyclometer calibration. I calibrate
my cyclometers with a simple one-rotation roll-out measurement. If I
change tire sizes or brand, I will (eventually) repeat the roll-out, but it
may take weeks...
Only once have I used a condiment for unnatural purposes. %^P I
put down a line of mustard on the driveway, rode through it and
measured the distance of three rotations. If I recall correctly, I didn't
change the cyclometer calibration number as a result.
I did happen to ride through a surveyed five mile "speedometer check"
section on a road a few years ago. My cyclometer read 5.02 miles.
That's less than one-half percent error...
Again, my point: cyclometers as simple wheel rotation counter devices
are quite consistent. If a cyclometer registers 102 miles on a 100 mile
course one day, it will likely read very near 102 miles on the same
course again (assuming tire size, pressure, etc... are the same). Knowing
this error rate, the calibration number can be adjusted to make the
reported distance more closely match the actual. (But who knows
the exact distance?)
GPS receivers are not-so-simple devices with inherent limitations that
can make their real-time trip odometer readings less consistent and
accurate. Their accumulated error in this reading, can be much larger
than their nominal position fix accuracy.
However, if you told me to ride 100 miles and then turn left on one of
a number of .25 mile spaced unmarked roads, I would much prefer to
have a GPS waypoint than simply a cyclometer/odometer!
Jon