The short course prevention factor adds 1 meter for every km which equates to 10m for 10km & 42.195 meter for the marathon.
When a course is measured, the measurer will incorporate the short course prevention factor into all splits.
Courses are measured using a direct drive mechanical device mounted on the axle called the Jones Counter. It counts approximately 11 counts per meter depending on tire size.
Before and after each measurement,the counter is calibrated against a straight line distance of at least 300 meters. This calibration course is measured with a steel tape taking into account the expansion of the tape due to temperature.
The measurer rides several times over the calibration course (minimum of 4). Knowing the average number of counts for the calibration course, the measurer can calculate the number of counts per mile. The measurer will then add the short course prevention factor for each of those miles. If the calculations determine that a mile = 18100 counts, approximately 18 counts will be added = 18118 counts per mile.
A post calibration is performed after the measurement and adjustments are made if needed.