pro s2n_plot,tot,s2n

   ; Read files
   files = dialog_pickfile(/multi,filter='*.fit')
   if (files[0] eq '') then return
   nfiles = n_elements(files)

   ; Declare storage
   tot = fltarr(nfiles)
   s2n = fltarr(nfiles)

   scr = get_screen_size()
   window,0,xsiz=scr[0]+100,ysiz=scr[1]+100
   ; read first file for setting box
   img = readfits(files[0])-100
   tvscl,img>100<200
   box_cursor,x,y,wx,wy
   window,1,xsiz=wx*nfiles,ysiz=wy

   for i = 0, nfiles-1 do begin
      img = readfits(files[i],header)

      ped = fxpar(header,'PEDESTAL')
      img = img + ped
      texp = fxpar(header,'EXPTIME')
      nexp = fxpar(header,'SNAPSHOT')
      tot[i] = texp*(nexp>1)
      sample = extrac(img,x,y,wx,wy)
      tvscl,sample,i
      out = moment(sample)
      s2n[i] = out[0]/sqrt(out[1])

   endfor

   s2n = s2n[sort(tot)]
   tot = tot[sort(tot)]

return
end