For each X-ray beam of the same nominal energy, the depth of Dmax along the central axis in water phantom at 100 cm TSD is within ±1. 5 mm of the average. For each X-ray beam of the same nominal energy, the relative dose at 10 cm depth on the central axis in a water phantom at 100 cm TSD (normalized to the dose at Dmax), within ±1. 0% of the average. See also Dmax.