I've been attempting to measure a half-marathon course with a Protege 8.0
over the past month. The roads I'm riding have suffered quite a bit from
a combination of near-record winter precipitation and delayed maintenance,
so there are lots of potholes, loose pieces of asphalt and other hazards.
Much of the the last 9 miles of the course is over streets with little
curbing and ample opportunities for the unintended acrobatic maneuvers
that follow inattention to a safe, shortest path.
The Protege 8.0, set up with 2 magnets and a circumference of 5000, seemed
problematic. According to my 2 most recent rides, 3/15 and 3/16/08, it seems
that I was off by 0.5, 1.0, or 1.5 full revolutions when measuring the same
mile. Here's the data (I omitted the first fractional segment):
Counts for calib #1: 772.650 revs
Counts for calib #2: 772.500 revs
MM Ride #1 Ride #2
-- ------- -------
12 772.650 772.325
11 772.650 772.300
10 772.650 771.000
9 772.650 771.900
8 772.650 772.075
7 772.650 771.025
6 772.650 772.400
5 772.650 772.300
4 772.650 772.175
3 772.650 772.550
2 772.650 771.925
1 772.650 772.275
Other details: Odometer was reset to 0 after putting 0 point on target line
and rolling forward about 1/4 rev so that upper magnet was in front of sensor.
The rim is marked into 40 equally spaced segments, so each mark is .025 revs.
Conclusion: I hope the new JR counter will fit on my front wheel.
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