anchor.diff:  DO
   
       READ (PDBFIL,'(A4)', IOSTAT=IERR) ATOM(1:4)
  +
  +    IF (ATOM .EQ. "ATOM") THEN
  +        BACKSPACE PDBFIL
  +        EXIT
  +    END IF
  +
       IF (IERR .LT. 0) THEN
           WRITE(STDERR, "(A)") "End of file reached with no ATOM records read."
           STOP
       END IF
   
  -    IF (ATOM .NE. "ATOM") THEN
  -        BACKSPACE PDBFIL
  -        EXIT
  -    END IF
  -
  -END DO
  -
  +
  +END DO
   
   ! Initialize statistics
   NATOMM = 0
  
positive.code: 
      READ (PDBFIL,'(A4)', IOSTAT=IERR) ATOM(1:4)
  
      IF (ATOM .NE. "ATOM") THEN
          BACKSPACE PDBFIL
          EXIT
      END IF
  
negative.code: 
  END DO
  
  
  MX = INT((XMA-XMI)/BOX) + 1
  MY = INT((YMA-YMI)/BOX) + 1
  MZ = INT((ZMA-ZMI)/BOX) + 1
  