###Compression###

     * What type of compression is available in ACS ?
     When HRC is prime and WFC is the auto-parallel, the buffer
     dump for the WFC parallel may occur during the next exposure. 
     A WFC buffer dump takes ~6 minutes, and most HRC prime exposures 
     will not be long enough to include both the WFC auto-parallel 
     and its associated buffer dump before the the HRC exposure ends. 
     When this occurs both images will be in the buffer at the same 
     time and since the WFC is not the prime science, one of the four 
     WFC quadrants will be compressed. Also, any data loss in the WFC 
     auto-parallel due to compression is considered routine and those 
     observations will not be repeated.