A peak-reading electrical instrument or meter

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 is one which measures the peak value of a waveform, rather than its mean

Arithmetic mean

In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...

 value or RMS

Root mean square

In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...

 value.

As an example, when making audio recordings it is desirable to use a recording level that is just sufficient to reach the maximum capability of the recorder at the loudest sounds, regardless of the average sound level. A peak-reading meter

Peak programme meter

A peak programme meter is an instrument used in professional audio for indicating the level of an audio signal.There are many different kinds of PPM. They fall into broad categories:...

is typically used to set the recording level.