Following the discovery of x-rays in 1895, doctors and physicists shared a common object of interest, and over the next decades, individuals from both worlds stressed the need for cooperation between physics and medicine in order for radiology to progress. But these calls for cooperation often also acknowledged the need for compromise, recognizing the very different values and goals of the two communities. In this talk, I will examine early debates over what constituted an appropriate measurement of a dose of x-rays for therapeutic purposes as a way of illuminating the divergent values of these two cultures. The ideal of medicine as an art, the unquantifiable skill of the physician, and a 'good enough' pragmatism clashed with physicists' emphasis on precision and objectivity. Tracing calls for a unit of radiation in both Britain and the United States, I will show that the voices of the x-ray physicists increased in authority over this time. Despite resistance from practicing physicians, physicists were successful in their push to establish their preferred unit, the röntgen, as the international unit of x-ray quantity in 1928.