This standard gives electroacoustical performance specifications for three kinds of sound measuring instruments: - a time-weighting sound level meter that measures exponential-time-weighted, frequency-weighted sound levels; - an integrating-averaging sound level meter that measures time-averaged, frequency-weighted sound levels; and - an integrating sound level meter that measures frequency-weighted sound exposure levels. Sound level meters specified in this standard are intended to measure sounds generally in the range of human hearing. Two performance categories, class 1 and class 2, are specified in this standard. A sound level meter may be a self-contained hand-held instrument with an attached microphone and a built-in display device. A sound level meter may be comprised of separate components in one or more enclosures and may be capable of displaying a variety of acoustical signal levels. Sound level meters may include general-purpose computers, recorders, printers, and other devices that form a necessary part of the complete instrument. Sound level meters may be designed for use with an operator present or for automatic and continuous measurements of sound level without an operator present.