Agreed, Pete. I rode a marathon course in Pensacola a couple of weeks ago in very cold temps (wind chill probably in the low 20s) and found the constants changed little, compared to a handful of feet difference and *very* minor constant change (.0002) on a 50-degree, drizzly day last week.
Thinking was the hardest thing...fortunately, we had two vehicles following to mark the locations and measure the particulars, leaving the RD and myself to freeze on our bikes.