The focal spot measurement jig consists of a cassette holder which can be set at any angle up to 20¡ã above the horizontal. Mounted on the cassette holder is a tower which holds a 1¡ã star pattern, supplied with the jig, giving a magnification factor approximately 2.5 x for an F.F.D. of 600mm. At the base of the tower is a centre-marker (a circular ring) which, when concentric with the star pattern image, indicates that the jig is correctly aligned to the central beam axis.
External Resources:
