Columns  Format        Description
===============================================================
  1-4      I4        Year 
  6-7      I2        Month
  9-10     I2        Day
 12-13     I2        Hour
 15-16     I2        Minutes
 27-30     F4.1      Critical frequency value in MHz
                     or letter:
                     A  blanketing 
                     B  absorption 
                     C  non-ionospheric (equipment) 
                     D  above upper frequency range of equipment 
                     E  below lower frequency range of equipment 
                     F  frequency spread 
                     G  ionization density too small 
                     H  stratification 
                     K  particle E layer 
                     L  no sufficiently defined cusp between F layers 
                     M  mode uncertain 
                     N  superimposed layers 
                     O  measurement refers to o component 
                     P  man-made perturbation of parameters 
                     Q  range spread 
                     R  attenuation near critical frequency 
                     S  interference 
                     T  interpolated 
                     V  forked trace 
                     W  above height range 
                     X  measurement refers to x component 
                     Y  lacuna (tilt) 
                     Z  measurement refers to z component 
========================================================================

At the end of data file there is the table in the following format: 

Columns  Format        Description
========================================================================
  1-2     I2         Hour of day
 10-16               Quartile 
 28-30    F3.1       Median
 42-43    I2         Number of accounting hours
 64-66    F3.1       Quartile range
========================================================================