3. EXAMPLE

My pre measurement calibration gives 351.35 rev. counts for a 671.53 m long calibration course which I have accurately measured (using a steel surveyors tape)

I measure the course and get 5,226 rev. counts

My post measurement recalibration gives 351.1 rev. counts for the same 671.53 m long calibration course

Calculate course length:

1. Pre measurement calibration = 351.35/ 671.53 rev. counts per m = 0.52321
2. Post measurement calibration = 351.10/ 671.53 rev. counts per m = 0.52284
3. Select the largest calibration constant = 0.52321 rev. counts per m
4. Course length = 5,226/0.52321 = 9,988.3 m

To make the course exactly 10 km I need to add (10,000-9,988.3) = 11.7 m

I can measure the 11.7 metres either with a measuring tape or using the calibrated bike.

Using the bike, 11.7 m will be 11.7*0.5231=6.12 rev. counts. We can measure the adjustment at either the start or the finish by riding the bike just 6.12 rev. counts.

How many significant figures should be used in the calculation? Enough so that the error is less than 0.01%. i.e about 10 times more accurate than our overall accuracy goal of 0.1%; We don't want rounding errors which we can avoid to add significantly to other measurement errors which are more difficult to eliminate. We could have used one less significant figure in the calculation of the adjustment and recorded 11.7 m as 12 m. However, it saves having to carefully think about rounding errors to make a habit of using at least one extra significant digit throughout all the calculations and then rounding for the final number.

Go to Page 4