The standard, as I have pointed out numerous times, as well as pointed everyone to the PPG photos/text of OEM paint application on our site shows, is that the clear is 1.5 to 2 mil in thickness, and THAT is what is important.
That,coupled with the poristy of the clear, only the top .5 mil being the dense portion, with the majority of the UV blockers is ALL YOU NEED TO BE CONCERNED WITH.
We do offer other gauges, ones that will read from composite, such as Vettes, etc, but they start at $4,000.00.
If one desires units that read wet film build, etc, start digging really deep, as they start at around $10,000.00 and go up to over $50,000.00
Ketch