Instrument Overview                                                         
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    This instrument name is used when a data set consists of observations     
    taken, usually over a long period of time, by various types of detectors  
    attached to one or more ground-based telescopes.  The VARGBDET identifier 
    is used when it is not possible or not practical to identify even the     
    generic type of detector associated with the individual observations      
    comprising the data set.  The published references listed in the          
    corresponding data set description may provide more information.