3.2.2 Distance Measurement
Since the calorimeter's construction principle relies on a self-supporting
structure comparable to a Roman arch a dimension precision in the order of
tenth of a millimetre for each module is indispensable. Larger discrepancies
would cause air gaps, deviations from the optimal shape and a poor or
impossible mechanical fit; as a result the acceptance correction would result
into a higher systematic error. The distance measurements to determine the
dimensional accuracy of the crystals were performed at PSI using the computer
controlled 3-Coordinate-Measuring-Machine from WENZEL Precision. It allows the
determination of positions with a precision of 7 µm. The touch head of the
machine was programmed to automatically scan the surface of a crystal; for each
plane 6 points were scanned. The angles between the planes are obtained, the
vertices of the crystal were calculated which then could be compared with the
specified values. A maximum deviation of 0.3 mm for a vertex and an angular
offset of 0.08° for opposite sides was tolerated.