Vernier zone

By means of a constant-delivery dropping-pipette fill a constant amount (between 0 05 and 0 1 ml) of each dilution of the standard and test samples into each of 8 cups cut in a large plate, using a predetermined Latin square design, or into one cup in each of 16 petri-dishes, and allow to stand at laboratory temperature for about one hour. Incubate for sixteen to twenty hours at a specified temperature (usually 32° to 37 ) and then read the zones of inhibition as accurately as possible by means of a projection magnification optical device or with vernier calipers. 

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