Abstract: A unit (11) with a length (L) is utilized in a device for indicating the position of an edge (7a) of a first area (7) which is irradiated by an x-ray radiation source (2) in relation to an edge (9a) of a second area, completely or partially coinciding with the first area, which second area is illuminated by a light source. The unit is provided with a first and second parts separated by a mark (12), which parts are intended to extend inside the second area and outside the second area respectively. The unit (11) comprises x-ray radiation-indicating elements (14, 22) that assume a first indication state in the presence of x-ray radiation (6) and a second indication state in the absence of x-ray radiation. The position indication can be determined by means of the said mark and indication states. The invention also relates to an arrangement and a method for the said position indication.

Abstract: Method and instrument for measuring X-ray radiation, for generating a value representative of the radiation in the form of an electric signal, such that the radiation at the measurement instance is caught by two photo-electric units each receiving the radiation after its passage through filters having mutually different degrees of absorption. The radiation value is computed on the basis of a ratio between the two generated electric signals. Adaptation of the signal intensity to a processing range is made, which constitutes a lesser part of the total intensity range of the signals generated by the radiation, by means of an amplifier device with a variable degree of amplification, by sensing the signal intensity after the amplifier device.