A reduction valve designed to be attached through a gastight connector (e.g., a pin-index or bull-nosed screw thread connection) to the valve stem of an calibration gas cylinder to lower high, variable gas pressure to a lower, constant working pressure, and may provide a pre-set flow rate of calibration gas for calibration of e.g., an anaesthesia monitor. It can be a single or a dual stage regulator, usually of a piston or diaphragm design. It will have a safety relief valve to avoid excessive pressure due to increased ambient temperatures, and it may have associated devices, usually a manometer or manometers, to display the available gas reserve of a gas cylinder and the working pressure.