How do you measure and state surface resistances of materials?

[Tunalover]

Folks-
Does anyone know how to measure and state surface resistivity of materials? We have two different classes of chemical conversion coatings used for aluminum and we need to express and measure surface resistivity for performance comparisons. The spec is MIL-C-5541 and the classes are:
-Class 1A for the best coating for corrosion resistance but the highest surface resistivity, and
-Class 3 for the worst coating for corrosion resistance but the lowest surface resistivity.

Is there a device and/or standard for carrying out the surface resisitivity measurements?

Thanks,
Tunalover