measure your mesh in an open area (or around the edges).. ie: 60 microns
now measure your mesh with emulsion on it, I like to do a few measurements to make sure that I'm consistent across the board... get your number (ie 75 microns)
divide 75 by 60 == 1.25 -> your EOM is 1.25
-or-
subtract emulsion+mesh thickness from mesh thickness then divide by the mesh thickness
(75-60)/60 = 0.25
both examples show that the EOM is 25%
if you really want to get geeky about it and track everything, you can download a copy of my emulsion tracking spreadsheet:
https://docs.google.com/spreadsheets/d/1bsqE6POiBiCCztbQZlCZIOG_TlYNbZRtJ6_x7aTcShI/edit?usp=sharingkeep track of your exposure time, thicknesses, eom, stouffer strip results, coating technique, and even get target exposure times based on the stouffer strip results.