def arc_degrees(arcminutes=0, arcseconds=0):
    """Calculate the decimal equivalent of the sum of ``arcminutes`` and
    ``arcseconds`` in degrees."""
    if arcminutes is None:
        arcminutes = 0
    if arcseconds is None:
        arcseconds = 0
    arcmin = float(arcminutes)
    arcsec = float(arcseconds)
    return arcmin * 1 / 60. + arcsec * 1 / 3600.