Relative transmission level - Definition

In telecommunication, relative transmission level is the ratio of the signal power, at a given point in a transmission system, to a reference signal power.

The ratio is usually determined by applying a standard test tone at zero transmission level point (or applying adjusted test tone power at any other point) and measuring the gain or loss to the location of interest. A distinction should be made between the standard test tone power and the expected median power of the actual signal required as the basis for the design of transmission systems.

Source: from Federal Standard 1037C in support of MIL-STD-188