Multiple Out/Back Courses from same Start/Finish

From what you have presented, I would do it the same way.

Which brings up a question that I thought of after reading another posting. That question is this: If one is measuring a true out-and-back on one trail, once you have reached the end (in this case, the 7.5km mark), that should be Ride 1, correct? Then, the return trip is Ride 2. Since you are confirming the location of each of the previously-identified points, why would this not fulfill the requirements of two rides?

I measured 5 km and 10 km courses with a common start/finish on a long bicycle path. Ride one was start to 5 km ( the 10 km turnaround ). Ride two was from the 5 km mark back to the start/finish. I marked kilometers on the way out and recorded counts at the kilometer marks on the way back. I did not use the sum of the shortest splits to adjust the 2.5 km and 5 km marks. Instead I used the counts from start/finish to the 2.5 km mark and the counts from the 2.5 km mark to back the start/finish to adjust the 2.5 km mark. Similarly for the 5 km mark.

Dale Summers
measurer

quote:

Originally posted by Duane Russell:
From what you have presented, I would do it the same way.

Which brings up a question that I thought of after reading another posting. That question is this: If one is measuring a true out-and-back on one trail, once you have reached the end (in this case, the 7.5km mark), that should be Ride 1, correct? Then, the return trip is Ride 2. Since you are confirming the location of each of the previously-identified points, why would this not fulfill the requirements of two rides?

I would agree, the ride out to the end turn-around would be Ride 1 and the ride back to the start/finish would be Ride 2.

quote:

Originally posted by Dale Summers:
I measured 5 km and 10 km courses with a common start/finish on a long bicycle path. Ride one was start to 5 km ( the 10 km turnaround ). Ride two was from the 5 km mark back to the start/finish. I marked kilometers on the way out and recorded counts at the kilometer marks on the way back. I did not use the sum of the shortest splits to adjust the 2.5 km and 5 km marks. Instead I used the counts from start/finish to the 2.5 km mark and the counts from the 2.5 km mark to back the start/finish to adjust the 2.5 km mark. Similarly for the 5 km mark.

Dale Summers
measurer

From my understanding, the sum of the shortest splits is not required but is the method I normally use. This would almost always make the course longer than using the single pair of counts as you indicated. Also, in Oklahoma, we almost always use 1 km splits instead of 1 mile splits.

I think the simplest way to think about this kind of measurement is:
1. Two measurements, each one stopping at all the points of interest.
2. For each interval, decide what is the best measurement (meters or decimal fractions of a km or mi).
3. Using these values, chart the present location of each of the points compared to where the point should be (this would of course depend on which end of the course is "fixed" and which can be adjusted).
4. Based on #3, make a list of "moves" for each point (e.g. "forward 2.1 m, back 0.5 m", etc.).
NOTE that you might or might not make all of these moves, but it is helpful to do a complete analysis to avoid mistakes in thinking about it. Personally I like to correct everything unless the change is only a foot or so-- this gives me a set of points that will be useful in case of future changes, etc.
This is probably what you have already stated and I'm just stating it another way.
Yes, going out can be one measurement and returning can be the second measurement. For out and back courses with a common start/finish line, this makes marking kilometers (vs. miles) very convenient.
Bob Thurston

Here is what my worksheet looks like when I want to make sure that each split is correct. If I was interested in only 5, 10 and 15 km, those would be the only splits I’d actually adjust.

Yes, the ride back is the second ride. Two measurements of the same thing.

I have ignored the 0.0008 here to illustrate the point. I believe it is unrealistic to expect distances less than 1 km to consistently get this sort of agreement.

Thanks to each of you for your feedback. Very much appreciated.

Since weather was so nice here Sunday, I decided to do the measurement. It took about 6 hours which included driving 70 miles. The course I was measuring is only 15 miles away but I haven't setup a calibration course near my house yet so have do some extra driving to/from the calibration course I am using for now.

I was able to mark off km splits and T/A points for 5km,8km,10km,12km,15km,20km,1/2 Marathon and 25km.
All the calculation appear to be good so was a valid measurement. Will head back to the course latter this week to make the adjustments and draw my diagrams.