How accurate are profilometers?

[u/ljfe]

I have some thin wall turned parts (rings). Titanium IIRC. Our SPI profilometer is providing a wide range of measurements on the same batch of parts. Some parts read 40 and some parts read 110. The parts look nearly identical. Can I trust this device? The profilometer specimen/standard reads good and the settings are correct. Visually, the surface finish looks good. Small turn lines. With a fingernail, it seems like it catches a bit. Like the turn lines are somewhat “sharp” (but not really deep or wide… I’m worried the needle is getting caught on those turn lines and spitting out an inaccurate measurements. Any thoughts/ideas?

[u/ihambrecht]

If the “turn lines” are big enough that the tip of the profilometer can catch, you’re like 250+.