The Gauge is the measurement set for the vertical rise of four courses of brickwork that is pre-set on a storey high gauge rod (approx. 50mm x 25mm) used from a datum levels set at each of the quoins. For the standard metric brick this is set at four courses to 300mm (10mm bed joint) but can be varied when a wide joint is specified. The thickness of earlier imperial bricks differed between manufacturers and, as a result, the Gauge could vary from 12 to 13.5 inches for four courses.