HP8568B__SetReferenceLevel (ul_pbar_instruments)

 *  Synopsis:
 *    #include <ul_pbar_instruments:hp8568b.h>
 *
 *    HP8568B__SetInputAttenuation( const CHP8568Bptr hp8568BPtr, const double attenuation )
 *
 *  Function intent:
 *    HP8568B__SetInputAttenuation() sets the scan reference level.
 *  Function parameters:
 *    double		attenuation	input attenuation in the range:
 *					  0 dB <= level <= +70 dB
 *  Function return value:
 *    CBS_OK		Setup was successful
 *    CLIB_INVARG	Invalid parameter value
 *    CLIB_GENERR	Unable to write HP8568B command(s) 
 *    CLIB_INVALID_DATA	HP8568B status error after GPIB command