I assume the question refers to the matrix below:
The numbers (1-5) relate to the ICAO code for expressing the friction characteristics of wet and precipitation covered runways. (ICAO Annex 14. ATT A, para 6). Code 6 is used for dry.
The codes relate to the estimated braking action (PIREP / ESF) and the observations on deceleration; however, the Airbus observations differ slightly from some other texts, and might represent industry's recent thoughts on runway condition reporting – Operational Landing Distances (OLD) and TALPA.
The code / runway descriptions should not be based on measured friction as it may be unreliable. Similarly PIREPS should only be used for downgrading a code due to their inherent subjectivity and dependence on aircraft type and pilot experience.
Refs
http://www.ukfsc.co.uk/files/Safety%...ust%202010.pdf and
Safety First 12