1.1 This standard concerns analogue electroencephalographs, which are defined as diagnostic medical instruments having at least eight channels. Such instruments are intended to accurately measure and record bioelectrical potentials and their time sequences as detected by electrodes attached to the surface of the human scalp. 1.2 This standard does not apply to information-processing electroence-phalographs, nor instruments that digitize the signals, nor other special-purpose instruments. 1.3 This standard is intended for the use of metrological services and other responsible governmental agencies. It specifies the metrological characteristics to determine methods of and equipment for testing, and initial and subsequent verifications of electroencephalographs that are regulated by laws. Metrological characteristics include errors in measuring voltage signals and time intervals as well as a number of other characteristics that affect measurement accuracy. Procedures are given for determining the relative error of measurement of sixteen instrument characteristics, and formulae are provided for calculating the associated permitted limits of these characteristics. These testing and control procedures provide a basis for ensuring that electroencephalographs of adequate accuracy are available for clinical measurements. The characteristics of the instrument covered are those that have been deemed to be important in order to achieve the necessary measurement accuracy in clinical practice, therefore, any changes in the requirements prescribed should be based on clinical experience and the needs of electroencephalography. 1.4 This standard does not address pattern approval, terminology, technical requirements, electrical safety and the associated test methods