Buffering capacity is determined by measuring the amount of moisture that is gained or lost by silica gel as the RH changes in the surrounding air, described by its M value. M is equal to the amount of water (in grams) that is gained or lost by 1 kilogram of silica gel for each 1% change in RH. For museum applications, where the case will cycle within a controlled RH range, the buffering capacity of silica gel is measured by its MH value, which takes into account changes in buffering capacity based on whether the RH increases or decreases. The M value or MH value of silica gel is important because it is used as the basis for determining how much silica gel must be added to the exhibition case.