anchor.diff:  ! Further revised by K.F. SMITH 17/7/91
   ! SGI version 1.00 A. S. Nealis 11/02/1992
   ! - Gives same volume for CA only and complete files
  -! SGI version 1.10 M. O. Mayans 22/02/1994 
  +! SGI version 1.10 M. O. Mayans 22/02/1994
   ! - Added carbohydrate support
   ! SGI version 1.15 M. K. Boehm ??/01/1995
   ! - Added SIA as a carbohydrate
  
positive.code:     STOP
  ENDIF
  
  ! Re-read file to populate our grid       
  
  REWIND PDBFIL
  
  ! Read in PDB file until ATOM found in cols 1-4
  DO 
  
      READ (PDBFIL,'(A4)', IOSTAT=IERR) ATOM(1:4)
  
  
negative.code:                EXIT
              ENDIF
          END DO
  
          DO NZ = 1, MZ
              ZB1 = ZMI + BOX*(NZ-1)
              ZB2 = ZMI + BOX*NZ
  