Virtually every estate in Domesday Book was rated for public obligations, the few exceptions being mostly royal estates. For each holding, a single assessment served all purposes: taxation, naval and military service, and other public responsibilities. As James Campbell has observed, this describes 'a fiscal machine whose existence might, without Domesday, have been asserted but hardly demonstrated' (The Anglo-Saxon state, page xi).
Although the units of assessment had different names in different regions, they had the same function everywhere. Each landowner in the country therefore knew his liability for every public duty. When the government needed to levy a tax or raise an army, all it needed to do was to announce the rate at which tax or service would be imposed. By multiplying this rate by the number of assessed units he owned, each landowner could calculate his liabilities, and any official could verify them. The system was simple, flexible, universal, and unique in medieval Europe.
For more detail, see J.H. Round, Feudal England (1895); Cyril Hart, The Danelaw (1992); Rosamond Faith, The English peasantry and the growth of lordship (1997); and James Campbell, The Anglo-Saxon state (2000).