anchor.diff:           else
               do j = 1,my
                  do i = 1,mx
  -                  sum(m) = sum(m) + q(i,j,m)*dxdy
  +                  y = q(i,j,m)*dxdy - c_kahan
  +                  t = sum(m) + y
  +                  c_kahan = (t-sum(m)) - y
  +                  sum(m) = t
  +                  !!sum(m) = sum(m) + q(i,j,m)*dxdy
                  enddo
               enddo
            endif
  
positive.code: c    # Output and diagnostics
  c    # ----------------------------------------------------------------------------------
        subroutine fclaw2d_clawpatch46_fort_conservation_check
       &      (mx,my,mbc,meqn,dx,dy,area,q,sum,c_kahan)
        implicit none
  
        integer mx,my,mbc,meqn
        double precision dx, dy, dxdy
        double precision sum(meqn), c_kahan
        double precision q(1-mbc:mx+mbc,1-mbc:my+mbc,meqn)
        double precision c, t, y
  
        include 'metric_terms.i'
  
negative.code:       cont = get_context()
  
        dxdy = dx*dy
        do m = 1,mfields
           if (fclaw2d_map_is_used(cont)) then
  C            sum(m) = 0
  c            c_kahan = 0
  