High Quality Content by WIKIPEDIA articles! A VU meter is often included in audio equipment to display a signal level in Volume Units; the device is sometimes also called volume indicator (VI).It is intentionally a "slow" measurement, averaging out peaks and troughs of short duration to reflect the perceived loudness of the material. It was originally developed in 1939 by the combined effort of Bell Labs and broadcasters CBS and NBC for measuring and standardizing the levels of telephone lines.