There are two models available: Standard and Pediatric. The Standard model has a light-gray switch plate and tests at 25db and 40db sound levels. The Pediatric model has a turquoise switch plate and tests at 20 db and 40db sound levels.
See the User Manual for a detailed explanation of the operation of the unit.
Every unit is calibrated on precision equipment and comes with a calibration certificate. The acoustic calibration criteria are traceable to the National Institute of Standards and Technology (NIST) for sound intensity.