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A compressed representation of the aspect solution as a sparse 3D histogram of the aspect solution giving the dead time and good time corrected exposure time versus RA, Dec, and Roll (expressed in offsets from the mean pointing). Changes in the SIM location relative to the mirrors are also included.

The aspect histogram is computed by the asphist tool. Since the period of the dither is slow (typically 700-1000 seconds) compared to how often it is readout (2.05 seconds) the change in aspect solution is often smaller than an ACIS or HRC pixel. By binning the aspect solution into an aspect histogram, tools run faster since they only process data at the unique aspect solution locations.

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