Each ASCII file has been created with columns of data. The first line of each ASCII file contains the column headers as defined within ISAP. These ASCII files may be read directly into ISAP so that you can begin your data reduction. For more information on how to read ASCII files into ISAP, see ASCII READ. Different observations will have different columns of data. The column headers most frequently used and their definitions are as follows:
| wave | Wavelength (microns) |
| flux | Flux (W/cm^2/um) |
| stdev | Standard Deviation of flux (W/cm^2/um) |
| det | LWS Detector number (0-9) |
| line | LWS Line number for L02 line scans (0-9) |
| rpid | Raster Point ID for raster observations (x,y); rpid=(256*x)+y |
The ISO LWS instrument had 10 detectors, covering different wavelengths with some overlap between adjacent detectors. For an L02 line scan observation, each line scanned had a designated line number. There is a corresponding "active" detector number. If an observation was an L02, the line and active detector numbers are given from the summary page. Together the two can be used to plot the lines that were scanned. There are four logical ways to separate data within these ASCII files, depending on the AOT. The table below shows how you may exclusively choose the data by matching up the the common values within these columns:
| L01 Pointed | L02 Pointed | L01 Raster | L02 Raster |
| det | line | rpid | rpid |
| det | det | line | |
| det |