VI. Techniques for special situations

1. Freezing the measurement

     Many times during measurement it is highly desirable to freeze the measurement process. For instance something may have fallen off the bicycle and it may be necessary to go back and retrieve it. A planned measurement at a specific mark may have been overshot.

    One simple and precise way of freezing measurement is as follows. Stop the wheel at about 0.1 rev past the zero spoke and break electrical contact by moving the computer slightly on its mount. (A switch placed in one of the leads can be operated instead. The Cat Eyes have a built-in switch.) Move the wheel back to the zero spoke and mark the position on the ground. To resume measurement line up the zero spoke with the mark, move the wheel forward about 0.1 rev, and re-establish electrical contact.

2. Correction for parked vehicles or other obstructions

    Shortly before the obstruction, stop the wheel at about 0.1 rev past the zero spoke and break electrical contact by moving the computer slightly on its mount. (A switch placed in one of the leads can be operated instead. The Cat Eyes have a built-in switch.) Move the wheel back to the zero spoke and mark the position on the road. Move the bicycle to clear the obstruction and align the the zero spoke  again with the mark preferably using a road seam as reference. Move the wheel forward about 0.1 rev, re-establish electrical contact, and resume measurement. When clear of  the obstruction repeat the process, but move back to the side of the road.

    A cruder method is simply to lock the front wheel with the brake and move the bicycle out or in from the side of the road.

3. Correction for overshoot of planned measurement

(i) Introduction

     The use of electronic counters greatly improves the clarity of readings and allows the repeated use of just one small value in the laying out of splits. The overshoot of a planned measurement is therefore likely to be a rare event as compared with the use of the Jones counter.

    Many correction strategies are possible many of which are similar  or identical with those used with the Jones counter and a few are described below. Basically, the number of revolutions back to the missed mark are counted. In the rare case where retention of the counter reading is desired, first freeze the counter reading as described above.

(ii) Overshoot in normal measurement of splits with rezeroing

    After stopping note the excess of revolutions on the counter. Roll the wheel backward through the zero point by the same number of times indicated by the excess, and continue on to the desired rim reading.

    The following are some examples of the above in the measurement of mile splits of 774.47 rev. Initial stop is at 774.97 rev: move the wheel backward a partial revolution until the rim reading is 0.47. Initial stop is at 776.97: move the wheel backward twice through the zero spoke and then on to a rim reading of 0.47.

    In the unlikely event that overshoot is a large number of revolutions proceed as follows. Move the wheel forward until the desired rim reading is obtained and mark the road. Note the excess revolutions on the counter, turn the bicycle around, align the zero spoke with the mark, move the wheel forward about 0.1 rev, rezero the counter, and ride back the excess number of revolutions.

    For example in the case of  a desired split of 774.47 but with an initial stop of 785.27: move the wheel forward to get a rim reading of 0.47 and mark the road; turn the bicycle around and, after the usual rezeroing procedure, ride back exactly 11 revolutions  as shown by the counter display and the rim.

(iii) Overshoot of a planned measurement point and retention of counter reading desired

    Stop the wheel at about 0.1 rev past the zero point and break electrical contact. Move the wheel backward and mark the road at the first zero point; from there count the number of times it passes through the zero point until it passes through the one beyond the desired measurement point. Move the wheel forward it is aligned with the point. The measured value is the rim reading plus the counter reading minus the number of times the wheel past through the zero point from the mark. Resume measurements at the first zero point as usual.

    The above procedure is a bit difficult if the overshoot is by a large number of revolutions. Fortunately, the chances of a measurer encountering this situation is extremely remote. Should it occur and an extra electronic counter is fitted proceed as follows. Stop the wheel at about 0.1 rev past the zero point and break electrical contact. Move the wheel backwards and mark the road at the first zero point. Turn the bicycle around and using the second counter measure back to the desired point. The correct value for the point is the first counter reading minus the second counter reading and the rim reading. Resume measurements at the first zero point as usual.

    Small backward movements can be done without recording impulses providing that a magnet does not pass through the sensor. This can be as much as a revolution in the general single or the special Protégé single magnet methods.