Fractions of a revolution can be read slightly faster and a more accurately when the wheel rim is marked in spoke intervals than with decimal markings. Also, spoke intervals are the obvious choice when the measurer has to set up his counter on a borrowed bike.
Previously I have described a program for the HP 33s hand-held calculator which allows rim readings only during calibration to be entered directly as hundredths of a revolution to get automatic calculation of the required data for course measurement (MN 133). With slight modification of the program, tenths of spoke intervals can be entered instead and the calculator outputs the fractions of a revolution the in same format.
Since one hundredth of a revolution is equivalent to 3.2 tenths of a spoke interval for a 32-spoke wheel, a divisor of 3.2 is added to the term for the sum of the rim readings. In fractional display, maximum denominator is set to 320 and fixed by setting flags 8 and 9.
For example suppose during calibration the following readings in spoke intervals are obtained:
18.6, 19.8, 18.6, and 19.8.
The following tenths are entered into the calculator :
186, 198, 186, and 198.
Output is then 2395.59 rev for 5-km and 771.07 rev for 1 mile, and activation of fractional display gives 2395 190/320 rev and 771 21/320 rev, respectively. For 5 km the fractional reading is 19.0, and for the mile, 2.1 spoke intervals.
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