The degree with which a measuring instrument obtains the "true" result. When noise measurements are carried out using a noise meter this will be the dB value representing the true sound pressure plus or minus the error at the time of the measurement. The acceptable limits for the accuracy (or error) of an instrument are usually specified in national and international standards issued by independent bodies such as ANSI or IEC. For noise meters they will cover frequency response, effect of the direction of sound arriving at the instrument and other various environmental effects such as temperature and ambient air pressure.