WAC 173-58-060
Equipment variation allowances. Due to
unavoidable variations in measurement sites and test instruments,
the following allowances shall be made for the respective sound
level meters:
± 1 dBA
for Type 1 sound level meters
± 2 dBA
for Type 2 sound level meters
This tolerance value shall be applied, after all necessary
calculations have been made, to the final reported sound level
for the measured sound source.