This chapter provides a short overview of some measurement signals that are useful to the sound engineer. The sinusoidal tone or sine wave is a practical test signal because it can be kept constant and because it contains one frequency at a time. It applies most of all to checking and calibration of audio meters and other audio equipment. Tone bursts at well-defined intervals are the foundation for checking level-reading instruments. Either burst generators or downloadable measurement signals are applicable. What is most important is that the frequency must be relatively high (5–10 kHz) if short bursts shall contain a sufficient number of complete periods. Broadband noise signals, primarily in the form of white noise and pink noise, which have constant energy per Hz and constant energy per octave, respectively, are indispensable in practical sound work. A click sound is a short impulse with a broadband spectrum. A click is also practical for examining echo phenomena in larger rooms.