This document provides an overview of sound level measurement using the testo 815 and 816 instruments. It discusses the basic concepts of sound level measurement including dB units, frequency weighting, time weighting, and accuracy classes. It also provides tips for proper instrument handling during measurement, including positioning the microphone at a zero degree angle facing the sound source and holding the instrument at least 30cm away from the body. Application areas for the instruments are listed as workplace measurements, industrial noise, environmental noise, and classification measurements.