How the autobrake system on the A320 is described in the FCOM is extremely sparse and IMHO insufficient. Crew calculate the landing distance for every landing and, in my experience, never notice how wildly inaccurate the computed data is. They are content that the landing was safe.
The AMM contains a lot more data and explains the systems better and as a result you can see why the QRH/ipad Airbus app is so inaccurate.