Various degrees of accurancy are required for the practical measurement of sounds of various kinds for different purposes. Hence, this standard specifies minimum requirements for three basic types of sound level meters, types 0, 1, and 2, with performance requirements that becomes progressively less stringent, proceding from type 0 to type 2. For each type, the standard requires three frequency weightings, A, B, and C, and two exponential-time-averaging characteristics, slow and fast. Also it defines a so-called impulse-response characteristic which is optional for any type. The standard permits special features in a sound level meter, such as pre-measuing capabilities, wide ranges for the display of sound level on an analog indicator, digital displays, recroding displays, and automatic range changing.