A quality of basic and fine matching of beams. For X-ray beams of the same nominal energy, the maximum dose in the plane normal to the beam axis at a depth of Dmax in water at 100 cm TSD is within ±1% of the average. For each beam of the same nominal energy, the dose at any point within the central 80% of the in-plane and cross-plane axes, normalised to the central axis, measured at a depth of 10 cm in water at a TSD of 100 cm is within ±2% of the average for the measured values at that point. This specification applies to X-rays at 10 cm depth and field dimensions greater than 10 x 10 cm2. See also Dmax.