Classes of measurement
Class A performance is used in applications that require precise measurements, such as verification of standards compliance or energy-settlement contracts. Parameter measurements performed using two separate Class A meters measuring the same signals, will produce matching results within the specified margin of uncertainty for that parameter.
Class S performance is used in statistical applications such as surveys or power quality assessments, possibly with a limited subset of parameters. Class S uses equivalent measurement intervals as Class A, but the Class S processing requirements are lower.
Class B performance is defined to avoid making any existing instrument designs obsolete.