1. A method of adjusting the resistance of a resistive memory element to a target value wherein said resistive memory element comprises a resistive layer located between two metallic electrodes and said resistive layer is formed of a host material which contains an active species which plays a substantial part in the conduction of an electric current and adjusts the resistance of the resistive layer; characterised in that the method comprises: (a) establishing a correlation between the duration of a pulse applied either to similar elements or to the same element and the resistance of the element after a pulse of said duration has been applied, (b) utilizing said correlation to determine the duration of pulse appropriate for producing the target value, and (c) applying a pulse of the duration specified by said correlation to produce said target value.