kuwait,
not sure about the airbuses but on the boeings, there are landing distance tables for different runway braking conditions and autobrake selections. select a conservative autobrake setting then compare the actual landing distance with the tabulated figures to 'guestimate' the braking action. i think this is a more academic method. however, braking action are just advisory and varies constantly. there's still no conclusive method of determining braking action to date. therefore, personally i always try to err on the cautious side
SR