Eom is the percentage of emulsion over the mesh.
Measure the mesh only, then measure the thickness of the emulsion on the mesh.
Use the formula
(Emulsion - mesh thickness) / mesh thickness
Will give you the percentage.
Ie:
I measured my emulsion thickness at 90 microns
I measured my mesh at 60 microns...
( 90 - 60 ) / 60 = .5
You can also shortcut by doing ( Emulsion thickness / mesh thickness )
90/60 = 1.5
Or 50% eom.