!     find which bin has biggest cumulative average
      subroutine decide(span,jm,jx,ipk,pk)
      use creep_module  
      implicit none
      integer:: span,jm,jx
      integer:: ii,i,j,nss,ipk
      real:: pk,aves,fn,w
      pk=0 ; ipk=(jm+jx)/2 
      do i=jm,jx           !scan saved data
       aves=0.0 ; fn=0.
       nss=ns(i) 
       do j=0,span-1        !lookback
        ii=(nss-j).and.31 ; w=wei(i,ii)  !bin, weight
        if(w.gt.0) then      !weight 0 => no data
         fn=fn+w ;aves=aves+d(i,ii)*w
        endif
       enddo
       if(fn.gt.0) then    !some data found
        aves=aves/fn
        if(aves.gt.pk) then
         pk=aves ; ipk=i
        endif 
       endif 
      enddo 
      return
      end