IX.  Correction for Overshoot Errors

1.  Introduction

     The use of the Protege counter as compared with the Jones will greatly reduce the error of overshoot. The Protege can be read comfortably while riding and the marking of splits with rezeroing involves only being alert for the same three-digit number on the meter repeatedly. In contrast the Jones can only be read after stopping the bicycle and the finish estimated from the last stop while riding. Moreover a different five-digit number must be used for each split.

    Notwithstanding the advantages of the Protege, correction of overshoot sometimes has to be made. With this type of correction, the Protege is sometimes at a disadvantage as compared with the Jones  in that unlike the Jones it cannot be run backwards. When overshoot is short and there is a parallel reference such as a curbstone, correction can be made by simply backing-up the bicycle and the Jones is at an advantage. However, when overshoot is long there is no parallel reference, the bicycle must be ridden back and the advantage lies with the Protege.

     Presented below are some correction methods. The precise method selected will depend on whether overshoot is short or long, whether correction is being made for a specific measurement value or a marked point, and whether retention of overall measurement is desired.

2.  Return to last point measured

     Returning to the last point measured is one of the simplest corrections for overshoot. Usually it involves only rezeroing and no calculation before remaking the measurement. This is in contrast with the Jones where a new table of values has to be calculated.

3.  Specific measurement value

(i) Back-up

1. Note the excess number of revolutions.

2. Roll back through the zero point on the rim for the same number of times as the excess number and on to desired fraction of a revolution..

3. The meter can be used to count the number of times through zero. First roll forward through zero and rezero the meter.

(ii) Ride-back

1. Adjust wheel position to get reading for desired fraction of a revolution and mark on ground.

2. Note excess number of revolutions.

3. Turn bicycle around, place rim zero on the mark, back-up slightly, rezero meter, and ride for the excess number of revolutions.

 

4.  Specific mark or point

(i) Back-up

1. Note the meter reading at stop.

2. Roll back to the mark or point counting the number of times passing through zero.

3. The meter can be used to count the number of times through zero. First roll forward through zero and rezero the meter.

4. Desired measurement = reading at stop - number of times through zero + rim reading at mark

(ii) Ride-back

1. Note the meter reading at stop, back-up to the rim zero, and mark ground.

2. Turn bicycle around, place rim zero on the mark, back-up slightly, rezero the meter, and ride to mark or point.

3. Desired measurement = reading at stop - final meter reading + rim reading at mark

 

5.  Retention of overall reading

      If retention of overall measurement is desired during correction in the methods described in 3 and 4, use the suspension-of-measurement method described in Section VII. If necessary use the meter in the second-circumference mode.