For any one interested in an explanation of the measurement of the Haliburton Forest Course here it is ...

12k course is >= 12k (>=6k x 2) (>= 6006m x 2)
26k course is >= 26k (>= 13k x 2) (>= 13013m x 2)
50k course is >= 50k (>= 25k x 2) (>= 25025m x 2)
50M course is >= 50M (>= 25M x 2) (>= 40274m x 2)
100M course is >= 100M (>= 25M x 4) (>= 40274m x 4)

calculated as follows:

all measurement is done in metric with a conversion factor of 1.609344 km / mile

As per CAU and IAU guidelines, GPS measurement shall be deemed official for Trail races. A short course prevention factor of 0.1% will be added to the event distance.

The trails will vary slightly from year to year and the course will be verified by GPS a minimum of once per summer prior to the race with any variations due to trail changes accounted for in the 50k, 50M, and 100M events at the turnaround locations. The GPS measured distances agree remarkably well with course measurements done in 2003 using a measuring wheel (within 0.25% (approx 100m over 40km)).

Course distances are measured in the following segments (keep in mind that while aid station locations may vary slightly from year to year it has no effect on the overall distance of the events):

Start to Aid Station #2
Aid Station #2 to Aid Station #3
Aid Station #3 to Aid Station #2
Aid Station #2 to Aid Station #4
Aid Station #4 to Aid Station #5
Aid Station #5 to the beginning of Black Creek Trail
Black Creek Trail to the 50k turnaround
Aid Station #5 to Aid Station #6
Aid Station #6 to Aid Station #7
Aid Station #7 to Dutton Road
Dutton Road to the 50M/100M turnaround

The "sanitized" gpx files which will be made available for the course are not the official course measurements. The official gps files have been smoothed and cleaned up a bit and are a presented as a guideline rather than being 100% accurate.
(and yes, I know it is meaningless to report GPS measurements on trails to the metre but when the total course was split apart into segments these are the resulting values and rounding them off would only introduce more error)

12K26K50K50M100M
Start - AS#220902090209020902090
AS#2 - AS#3380738073807
AS#3 - AS#2585858585858
AS#2 - AS#440944094409440944094
AS#4 - AS#57511751175117511
AS#5 - Black Creek Trail1015
Black Creek Trail - 50k turnaround650
AS#5 - AS#661216121
AS#6 - AS#799989998
AS#7 - Dutton Road9898
Dutton Road - 50M/100M turnaround700700
Total618413695250254027740277