There are 5 levels of quality, detailed as follows: Measurement of audio speech-to-noise ratios in a way which reflects interfering effects in a meaningful manner is difficult for the kinds of noise often encountered at mobile system receivers.
For this reason and as a matter of convenience, a subjective rating of the interfering effect of the noise using the term “circuit merit” is commonly used in place of metered measurements.
It is intended to be used on a statistical basis, by collecting multiple data points (either subjective scores by human listeners, or by electronic measurements), to then produce a comprehensive report on the circuit quality.
This belief is contrary to the published description of the R-S-T System (which uses the same number of levels for readability), and of modern (as of 2006) requirement "...that plain language be used for multi-agency, multi-jurisdiction and multi-discipline events, such as major disasters and exercises..." instead of numeric codes in radio traffic in NIMS/ICS.
[11] As both Circuit Merit and the R-S-T System use numbers that are often difficult for operators to map to meanings, neither complies with the intent of the NIMS plain language directive.