Latin ad pensum, ad pondus
Payment of some of the larger manorial valuations - notably on royal manors - was made by weight, 240 silver coins constituting a pound sterling. The procedure avoided loss to the crown due to debasement - wear, clipping, etc. - and also eliminated any arithmetical error due to counting large numbers of coins. Alternatively, an arbitrary allowance was made for the supposed debasement.
For further detail, see Sally P.J. Harvey, 'Royal revenue and Domesday terminology', Economic History Review, second series, vol. 20 (1967), pages 221-28, and Sally P.J. Harvey, Domesday: Book of Judgement (2013), chapter 6 and appendix 1.