I originally used them to confirm a temp related shift that was pretty fast moving on the gun... it would typically react to a degree change with a click within 10 mins or so... if I went from a cold shaded, say on a summer's morning, then onto somewhere bathed in sunlight, the gun would shift.
that seemed to be caused by a soft valve seat, and once that was changed, it stopped... well sort of. I still see shifts, but the zero holds for the duration of the day irrespective of temp.
All i can say i've found is that when it's cold the shots go low, and when it's hot, they come up. I rarely see anything attributable to that on the chrono, so it's either something bending, or air density.
I'll get to the bottom of it one day, but my suspicions are now that beyond mechanical distortion and changes, air density might have more to play than i thought.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep