This signal type provides a number of predefined linear combinations of the calibrated signals above. For instance, the segments of the silicon detector can be combined to yield bright field contrast (sum of all segments) or differential phase contrast (difference of opposing segments), or you can look at a single segment (which is not really a combination any more, but they are still included).
This signal type gives you again a 3-dimensional dataset, but the size of the third dimension is not the number of recorded signals any more, but rather the number of combinations defined. See Sec. 9.4 for details.