This standard applies to direct acting recording electrical measuring instruments for direct and alternating electrical quantities, which are used for recording the varying valus of one or more measures quantities as a function of time. It applies to strip, drum and disk recording instruments, viz: -- ammeters -- voltmeters -- single-phase and polyphase wattmeters, varmeters, phasemeters and power-factor meters (active or reactive); -- frequency meters; -- ohmmeters It also applies to certain accessories used with such apparatus, viz.: -- shunts --series resistors and impedances. Where others accessories are associated with instruments in as much as the calibration has been made of the instrument together with the accessory, the standard is applicable to the combination of instrument and accessory. This standard also applies to electrically operated measuring provided that the electrically operated measuring instrument (reciver) only considered, and that the relationship between the non-electrical quantity and the electrical one is known. It also applies to recording instruments, together with thier non-interchangeable accessories, having electronic devices (other than rectifiers and diodes) as listed in Sub-clauses 1.3.1 to 1.3.3, provided that they are marked with symbol(s) F-20 and/or F-21.