Next: Column NDETUSED
Previous: Column FILTCODE_n
If ``neutral'' filters are used, their quantitative effect should be stored in
a column named NDVALUE.
The real number stored here should normally be the factor by which the
intensity measured through the ND filter should be multiplied to be on the same
scale as data taken without the ND filter.
Therefore, the numbers are normally all bigger than unity, except for the
un-attenuated passbands, for which one normally puts unity in this column.
Because ``neutral'' filters are not really neutral, the value will differ
somewhat from one passband to the next.