SPI Ge detector arrangement and shadowgrams from the mask. The 19 Ge detectors of the SPI camera are arranged in a densely packed hexagonal configuration (top). Detectors are numbered inside-out, starting from 0 for the central detector. Shadowgrams are cast by the mask onto the Ge camera. The figure set below shows these shadowgrams for a point source on axis, and for the 25 telescope reorientations in steps of 2.1 degrees (pointings) that comprise a standard 5 × 5 dither pattern. Intensity received by each detector is colour-coded from black (none; shadowed) through red, yellow to white (full exposure).