Reed Instruments R8090 (SC-05) Sound Level Calibrator for 1/2" Diameter Microphones, +/-0.5dB Accuracy Generates stable acoustic signal at a controlled frequency and amplitude to verify the accuracy of your sound level meter Simply place calibrator on microphone, turn on and adjust your sound level meter Output sound pressure levels of 94dB and 114dB Accuracy of +/-0.5dB Accomodates 1/2 inch diameter microphones