IMO, establishing criteria for measurements needing no post-cal makes sense to me. The purpose of the post-cal is to bracket the extent of tire size and counts as road and air temperatures vary during measurement, and then to make adjustments to the course to eliminate the possibility of a short course. If the ambient temperature during measurement stays the same or increases until measurement is over, it seems to me a simple "Russell Check" to verify that the counter constant has not increased should suffice.
Unlike Mark, I often find higher post-cal numbers, due to the time of day I tend to start measuring - rarely in the early morning. If the temperature increases, then decreases by the end of the measurement ride, or fluctuates during a long measurement, such as a marathon measurement, a cooler post-cal could result in a third entire re-measurement. A situation to be avoided. In this instance, when temperature fluctuations during measurement (sun going in and out of heavy clouds, a passing thunderstorm) or a cooler (e.g. late day) post-cal are expected, clearly our pre-cal numbers aren't going to be as accurate as we would like. In this instance, using pre-cal or even an average constant could in theory result in an inaccurate, even a short course. Or, even if the overall measurement is accurate, some mile or kilometer splits could be less accurate than we might prefer. Who here hasn't run a race in which well-placed mile markers resulted in some of your split times being unexpectedly higher or lower?
Since we know the SCCF is in place to accommodate the probability of more "wobble" during measurement than during calibration, and of our necessity to swerve around potholes or other small obstacles on the course tangent while riding, would it make sense to increase the SCCF slightly to anticipate such temperature/constant fluctuations?
It is interesting to me that, calibrating over a wide span of temperatures results in such a small change for me in mile constant counts. In my experience, a range of ~ 17,985 in warm weather to ~ 18,030 in cold weather is about as much as I have seen. Maybe using 100% nitrogen in my tires helps contain the variation. I would guess that Duane, using his solid rubber tires, experiences even less. I would like to hear from other measurers what the range of their constants has been, given the same tire. My reasoning is that increasing the SCCF by some small increment could account for temperature fluctuations that could otherwise materially shorten a course.
Consider the case of a marathon measurement: if the post-measurement temperature is lower than the pre-cal temperature by more than a few degrees, the inaccuracy mave well have accumulated over the day. Maybe, say, mile 10 is only 2 feet short of where a theoretical "perfect" constant-temperature would place it. But, as the temperature fluctuates, or decreases, subsequent miles are off, too. Over the next 16 miles, the error adds up to more than .08%. So, you have to measure the entire course again. Here, the same or a similar temperature variation could occur. All we have then done is repeat the "erroneous" measurement. In the instances when a post-cal (after the second ride) reveals a higher number of counts, we then move the Start, Finish, and/or a turnaround, which then makes at least one mile split - usually the last mile - a good bit longer, for a marathon, than any other. I know I have run many races on certified courses in which the last mile was a good bit longer than the rest. I am taking into account the possibility of fatigue and terrain in the last mile in making this assertion.
I would like to explore the non-trivial feasibility of changing the SCCF. We have established no official criteria for "too long". Historically, some validation measurements have revealed courses with a little "extra" distance - beyond the SCCF, of course. I do not have sufficient data to back up any specific recommendation for how much to change the SCCF to ensure we subsume temperature variations or decreases during a measurement ride.
I would like to hear thoughts from anyone on this board about this opinion. If, for instance, we were to double the SCCF, we would then have slightly more than 10 feet per mile to be "eaten up" by the full complement of wobbles, potholes, and cooling or fluctuating temperatures. Measure with a .002% SCCF, then perform and pass a "Russell Check", and voila - no post-cal or further course lengthening.
This would be a proverbial "good thing".