 In the past, alternate subunits were used in historical electronic books; "mfd" and "mf" for microfarad (µF); "mmfd", "mmf", "µµF" for picofarad (pF); but are rarely used any more.Capacitance can be calculated if the geometry of the conductors and the dielectric properties of the insulator between the conductors are known.A qualitative explanation for this can be given as follows.