def define_additional_meta(nlamps=20):
    """
    Defines meta that tends to be instrument-specific and not used as
    widely in the code.

    See :func:`define_core_meta` for additional details

    For meta used to define configurations, the rtol key specifies
    the relative tolerance for a match

    Args:
        nlamps (:obj:`int`, optional):
            Number of calibrations lamps for this instrument.

    Returns:
        :obj:`dict`: Describes the additional meta data used in
        pypeit.
    """
    additional_meta = {'dichroic': dict(dtype=str, comment='Beam splitter'),
                       'filter1': dict(dtype=str, comment='First filter in optical path'),
                       'dispangle': dict(dtype=float, comment='Angle of the disperser', rtol=0.),
                       'hatch': dict(dtype=str, comment='Position of instrument hatch'),
                       'slitwid': dict(dtype=float,
                                       comment='Slit width, sometimes distinct from decker'),
                       'detector': dict(dtype=str, comment='Name of detector'),
                       'arm': dict(dtype=str, comment='Name of arm (e.g. NIR for X-Shooter)'),
                       'datasec': dict(dtype=str, comment='Data section (windowing)'),
                       'idname': dict(dtype=str,
                                      comment='Instrument supplied frametype (e.g. bias)')}
    for kk in range(nlamps):
        additional_meta['lampstat{:02d}'.format(kk+1)] \
                = dict(dtype=str, comment='Status of a given lamp (e.g off/on)')
        additional_meta['lampshst{:02d}'.format(kk + 1)] \
            = dict(dtype=str, comment='Status of a lamp shutter (e.g closed/open)')
    return additional_meta