How you measure and what you use to measure makes a difference, of course.
I have 2 sets of calipers and one micrometer. The calipers are 2 with dials and one without. These 4 measuring tools give me 4 different measurments on any given piece of cloth.
I measure with exactly the same technique when using each set of calipers but rarely use the non-dial calipers. I have to use a head loop magnifyer to read it with any accuracy. The difference in the calipers is a very minute difference in the width of the jaws- I assume. The measuring system with them is to squeeze the tines together on the material, between my forefinger and thumb - as tightly as I can and exactly the same each time. My measurements are smaller than most anyone else's due to this tight squeezing - again, I assume. I figure the rifling lands do this to the patched ball combination and thus that gives me a more accurate measurement for when adding ball diameter, and patch thickness together to see if any given patch even remotely has a chance of working. This system works for me.
With the micrometer, I spin the barrel's rathet until it ratchets a number of time brrrrrrrrt. The mic gives thinner readings than any of my callipers, by .002" on the closest calipers to .005" on the pair giving the largest reading. Because of these various readings, I most commonly use one set of calipers, the ones giving the thinnest readings.
Thus, my .023" patches (red/white/blue/blue ticking) might be upwards of .024" to .028" for other people measuring. I measure washed 10 ounce denim at .0225". The 12 ounce denim (VERY heaviest 100% cotton jean material used) I use in my .69, runs up to .031" with calipers, but only .025" with my mic - so that's what I call it.