Column NDVALUE

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.