Abstract: An X-ray measurement device (20) is disclosed which utilizes a pair of detector units (29, 30) which receive X-rays through filters (40, 41) of differing attenuation of X-rays. The detector units preferably include two pairs of photodiode detectors arranged symmetrically in four quadrants with the diodes in each detector unit in diagonally opposite quadrants, thereby minimizing the effects of changes in orientation of the device with respect to the axis of the X-ray beam. The outputs of the detector units are passed to variable gain amplifiers (42, 43) the gains of which are automatically adjusted to bring the output voltages within a desired range, and the outputs of the amplifiers are integrated by integrators (49, 50).