RECEIVER /DEROTATOR

    /DEROTATOR angle system

    Specify derotator angle for HERA

    Real      :: angle             ! in units [deg] (!)
    Character :: system            !

    Choices for system:
    "Nasmyth"
    "horizon"
    "equatorial"
    "frame"                        ! same as Nasmyth
    "sky"                          ! same as equatorial

    NOTES: The last 2 are for consistency with old control system and HERA conve
    This option works only for RECEIVER HERA1 or RECEIVER HERA2 (of course it's
    same angle for HERA1 and HERA2).