Abstract: In one broad aspect, the invention provides a method of receiving instructions for an implement, for example, a drill string stabilizer, mounted on a drill string, which instructions are transmitted by varying the rate of flow of, or pressure exerted by, the fluid in the bore of the drill string in accordance with one of a plurality of predetermined sequences; the method comprising the steps of:a) monitoring variations in the rate of flow of, or pressure exerted by, the fluid in the drill string;b) comparing the sequence of monitored variations with a plurality of predetermined sequences, each predetermined sequence corresponding to a set of instructions for the implement; andc) eitheri) ignoring the variations if they do not correspond to a predetermined sequence, orii) if the variations do correspond to a predetermined sequence, executing the instructions which correspond to that sequence.