1. Introduction
Spurious impulses should not occur if the measurer remains alert and glances at the meter and/or at the bottom of the rim to avoid stopping on the zero point. However, while finding the way on the first ride around a course, it is easy for the measurer to get distracted and stop without doing this. By unlucky chance, he may stop right on the zero point and rock the wheel back and forward so that an unknown number of impulses may be generated. I f he then realizes what he has done, a correction can be made by returning to the last defined point, but if he does not, it may not be obvious until the results of the second ride are compared.
Fortunately, the above problem can be avoided by using two electronic counters simultaneuosly. (This can be a cheap solution since the Protege 5 can be purchased for as little as $10 from biketiresdirect.com.)
2. Setup
Mount the sensor for the secondary counter above or below that for the primary counter, but place the secondary magnet four spokes behind that for the primary magnet on the same side. (The secondary counter will then increment at a rim reading of 0.2 rev.)
3. Operation
Align the zero point of the rim to the starting point, roll back about three inches, and zero both Protege meters. At the end of the ride, rim reading is the same for both meters, but if this is less than 0.2 rev, add one to the secondary meter reading. Should the meters not agree, this is probably because of spurious counts generated from an intermediate stop, and the smaller reading should be used.
4. Discusssion
The above setup should be reassuring to measurers that if they mess up no time will be lost. It should be reassuring to some measurers who evidently still believe that the detectors do not detect all impulses. Also, it is insurance against battery and electronic failure.
Note that the Jones meter sometimes fails without being immediately obvious, but it is not practical to use a secondary meter.
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