A Fortran line is divided into fields for the required information.
  Each column represents a single character.  You cannot specify a
  sequence number field using this method of coding.

   COLUMN   FIELD
   ------   -----
   (before tab)
     1      Indicator: Comment(C,c,*,!,blank) or Debug(D,d)
   1-5      Label (any decimal integer except zero)
   (after first tab)
     6      Indicator: Continuation of statement (any digit 1-9)
   (after second tab)
            Statement Field (up to column 72)

  Tabs are treated as single characters.