In addition to the image files, the .trl or trailer file-which comes with each FOC observation-is an ASCII text file that describes the standard processing applied to the images by OPUS. The .pdq file reports any real-time activities associated with the observation, such as slews for an interactive acquisition, and any problems that might have occurred with the telescope, such as a guide star acquisition failure or guide star recenterings. The standard header packet (.shh and .shd files) contains information about the scheduling of the observation. The data quality files (.q0h and .q0d), in principle, would contain information on position of blemishes in FOC images. However, they are not used by the FOC because these positions vary with time, limiting the utility of these files. The unique data log files (.ulh and .uld) contain engineering information not generally of interest to most observers.