An easement may arise by a number of means: express grant, by necessity (where, for example, a vendor sells land to a purchaser which would otherwise be inaccessible as a result of being surrounded by land which he retains) or by prescription. It is with that last method of acquisition that this question is concerned. See Practice Note: Easements—nature and characteristics. After use for a certain time, the law presumes there to have been a grant. There are three methods of calculating time: two at common law and one under the Prescription Act 1832 (PA 1832). Before considering the periods of time, it is useful to set out the types of activity which must be shown to have existed. Unless and until they have occurred, there can be no question of time starting to run. The user must be what is often described as nec vi, nec clam, nec precario, that is to say: