CONDUCTIVITY TERMINOLOGY Both AG-5 and AG6/PH AGRI-METERS are calibrated in millimhos, the term most widely used by growers to express electrical conductivity. Some charts may read in other units called micromhos. However, since one millimho equals 1,000 micromhos, conversion is easy. Parts per million (ppm) is also sometimes used. Conductivity/ppm fertilizer concentration tables can be obtained from your supplier, consultant, or university advisor.