anchor.diff:  C        This subroutine provides Effective Total Mass Density for
   C        output D(6) which includes contributions from "anomalous
   C        oxygen" which can affect satellite drag above 500 km.  This
  -C        subroutine is part of the distribution package for the 
  +C        subroutine is part of the distribution package for the
   C        Neutral Atmosphere Empirical Model from the surface to lower
   C        exosphere.  See subroutine GTD7 for more extensive comments.
   C
  
positive.code: C          SUBROUTINE GTD7D -- D(6) is the "effective total mass density
  C          for drag" and is the sum of the mass densities of all species
  C          in this model, INCLUDING anomalous oxygen.
  C        
  C     SWITCHES: The following is for test and special purposes:
  C          
  C        TO TURN ON AND OFF PARTICULAR VARIATIONS CALL TSELEC(SW),
  C        WHERE SW IS A 25 ELEMENT ARRAY CONTAINING 0. FOR OFF, 1. 
  C        FOR ON, OR 2. FOR MAIN EFFECTS OFF BUT CROSS TERMS ON
  C        FOR THE FOLLOWING VARIATIONS
  C               1 - F10.7 EFFECT ON MEAN  2 - TIME INDEPENDENT
  
negative.code: C        D(2) - O NUMBER DENSITY(CM-3)
  C        D(3) - N2 NUMBER DENSITY(CM-3)
  C        D(4) - O2 NUMBER DENSITY(CM-3)
  C        D(5) - AR NUMBER DENSITY(CM-3)
  C        D(6) - TOTAL MASS DENSITY(GM/CM3) [includes anomalous oxygen]
  C        D(7) - H NUMBER DENSITY(CM-3)
  C        D(8) - N NUMBER DENSITY(CM-3)
  