IEC 60052 sets forth recommendations concerning the construction and use of standard air gaps for the measurement of peak values of the following four types of voltage : a)Alternating voltages of power frequencies; b)Full lightning impulse voltages; c)Switching impulse voltages; d)Direct voltages. Air gaps constructed and used in accordance with this standard represent IEC standard measuring devices in accordance with IEC 60060-2 and are primarily intended for performance checks of high voltage measuring systems .