pro fit_relvis,f,rv,isamp,siz

   nf = n_elements(f)
   s = [43.,74.,93.,33.,92.,28.,37.,26.,48.,70.,32.,50.,51.,144.,48.]
   sx = findgen(300)+5.
   if (n_elements(siz) eq 0) then siz = fltarr(nf)

   for j = 0,nf-1 do begin
      sscl = (s*5/f[j])^(-2)
      if (siz[0] eq 0) then begin
         plot_io,sscl,rv(*,j,isamp),psym=1,$
            yran=[0.01,10],xran=[0,max(sscl)*2]
again:
         read,'Enter a source size [0 to accept previous]:',asec
         if (asec eq 0) then siz[j] = asecp else begin
            asecp = asec
            oplot,sx^(-2),exp(-(!pi*asecp/sx)^2)
            goto,again
         endelse
      endif else begin
         if (j lt 18) then begin
            !x.tickname=[' ','71',' ','41',' ','32']
            plot_io,sscl,rv(*,j,isamp),psym=1,$
               yran=[0.01,10],xran=[0,0.001]
         endif else begin
            !x.tickname=[' ','22',' ','13',' ','10']
            plot_io,sscl,rv(*,j,isamp),psym=1,$
               yran=[0.01,10],xran=[0,0.01]
         endelse
         !x.tickname=['','','','','','']
         xyouts,0,3,string(f[j],format='(F4.1," GHz")')
         oplot,sx^(-2),exp(-(!pi*siz[j]/sx)^2)
      endelse
   endfor

   plot_oo,f,siz,psym=2,yran=[1,100],xran=[1,20],xsty=1,ysty=1,$
      ytit='Source size (arcsec)',xtit='Frequency (GHz)'

return
end