CEM SC-05 Sound Level Calibrator for 1/2" Diameter Microphones, +/-0.5dB Accuracy Dual sound pressure outputs at 94dB and 114dB which can be selected by a switch. Operates on a single 9V battery.Auto sound off on low battery to ensure accurate performance. Output sound pressure levels: 114 dB and 94 dB Output frequency: 1000Hz +/- 4% Reference conditions: temperature at 23 deg C (73 deg F); Air pressure at 1013 mbar; Humidity at 65%RH