anchor.diff:            if (mod(expflg,10).eq.0) then
                 nx = int((x2-x1)/dx+1.0d-6)+1
             else
  +              if (dx.le.1.0d0) then
  +                  call usage('!! Error: in exponential mode, DX must '//
  +     1                       'be greater than 1')
  +              endif
                 nx = int(dlog(x2/x1)/dlog(dx))+1
             endif
         elseif (nx.le.1) then
  
positive.code:      2            '-y Y1 Y2 [-ny NY|-dy DY] -RX1/X2/Y1/Y2'
        write(*,*)
       1 '            [-z Z|-dip X0 Y0 Z0 STR ',
       2              'DIP|-xsec X0 Y0 AZ [-xz]]'
        write(*,*)
       1 '            [-clip XYFILE] [-o OFILE] [-p] [-h]'
        write(*,*)
  
negative.code:           if (expflg.lt.10) then
                ny = int((y2-y1)/dy+1.0d-6)+1
            else
                if (dy.le.1.0d0) then
                    call usage('!! Error: in exponential mode, DY must '//
       1                       'be greater than 1')
                endif
                ny = int(dlog(y2/y1)/dlog(dy))+1
            endif
        elseif (ny.lt.1) then
  