Methods for enhancing blood and lymph flow in the extremities of a human subject are disclosed. A digital logic circuit, such as a D-type flip-flop, is provided with a phase signal and clock signal having a frequency relationship. The armoured flexible pipe according to the invention is especially advantageous for use in the extraction, transport or refining of mineral oil or related fluids. The suture cutter may include mechanisms which can be used to push and position a knot, so that a single device may be used to both push a knot and trim the excess material therefrom. The diffraction grating is manufactured by processing a data stream indicative of the image.