Now you have your data, and are ready to reduce them.
Table 
gives a list of the files you will need.
Table: Checklist of necessary table files
If you need to make supplemental standard-star files, refer to the
``Standard-star files'' subsection at the end of section .
If your data files use different names for standard stars than are used in
some existing standard-star file, you can just supply a ``program-star'' file
that contains your names for these stars; use MAKE/STARFILE to make this
table.
The reduction program will try to make the cross-identifications,
using positional coincidences as well as names
to decide which entries to match up.
If you were able to find additional information about the instrument while you were observing, be sure to add any missing information to the instrument file. The reduction program needs to have an accurate model of the instrument, as well as your procedure. You can check an existing instrument file by running MAKE/PHOTOMETER.
Next, you must convert your observational data to the format MIDAS can digest. If other people have already used the same equipment you did, there are probably programs available to do this conversion. If not, you will have to devise the conversion yourself.
In any case, you should look over the data files, line by line, to make sure there are no garbled records. Often, either equipment malfunctions, operator errors, or problems on reading and writing tapes convert some part of the data into nonsense. You cannot reasonably expect any file-conversion program to cope with nonsense, so edit it out first.
The sooner mistakes are removed from data, the less trouble they cause. Each data-logging system is likely to make its own peculiar kinds of mistakes; and each observer tends to make some particular kinds of errors at the telescope. Therefore, it is strongly recommended that users have their own preprocessing software, to detect mistakes and inconsistencies in raw data files, before running CONVERT/PHOT.
A common problem is an incorrect time or date setting; be particularly careful to correct any errors that were discovered belatedly while observing. Other common problems include misidentified stars; incorrect designations of star and sky measurements; missing or incorrect data in star files; and non-standard data formats.
In fixing errors in the data, always save a copy of the original in case you make a mistake while editing.