anchor.diff:  c      end of command line parsing
   c      ---------------------------      
   18     continue
  -       if(overb) then
  -         write(*,*) "Maximum Distance:",rmax 
  -         write(*,*) "Lattice vectors",(latv(i),i=1,3)
  -         write(*,*) "Number of bins:",nb
  -         write(*,*) "Input file(s)"
  -         do i=1,nfil-1
  -           write(*,*) trim(infile(i))
  -         end do
  -         write(*,*) "Output file",infile(nfil)
  -       end if
  -c       
  -c       rmax = 4.0
  -c       nb = 100
  -c       atom1_tag = " "
  -c       atom1_id = 3910
  -c       atom2_tag = "O"
  -c       latv = 10.0014453
  -c       file_lattice = "lat.dat"
   c      ---------------------------      
   c      start checks/balances
   c      ---------------------------      
  
positive.code:          gr = gr + gr0
           nf = nf+1
           if(nfrm.gt.0.and.nf.ge.nfrm) then
              write(*,*) "exiting because exceeded number of frames",nf,nfrm
              exit
           end if
         end do
  
negative.code: c     -------------------------------------
    100 continue
        read(fn,1000,end=11,err=911) card
   1000 format(a)
        if(card(1:5).ne.'frame') goto 100
  c
  c     skip one lines here
  c     --------------------
        read(fn,1000,err=911,end=911) card
  c     read lattice
        message = "reading lattice"
        do i=1,3
          read(fn,1000,err=911,end=911) card
          i0=1
          do k=1,3
            message = message(1:len_trim(message)+1)//token
  