HD2024 - Class 1 Sound Level Calibrator Sound level calibrator, class 1 according to IEC 60942:2003, suitable for ½” and ¼” (HD2020AD4 adaptor for ¼” microphones not included) standard microphones. Does not require any correction for static pressure, humidity and temperature. Calibration frequency 1000 Hz, levels 94 dB. For all the sound level meters. Available as well with ISO17025 calibration certificate according to IEC 60942 included (code HD2024C).