inline double UpscalerBase<Traits>::computeDelta(const int flow_dir) const
    {
	double side1_pos = 0.0;
	double side2_pos = 0.0;
	double side1_area = 0.0;
	double side2_area = 0.0;
	for (CellIter c = ginterf_.cellbegin(); c != ginterf_.cellend(); ++c) {
	    for (FaceIter f = c->facebegin(); f != c->faceend(); ++f) {
		if (f->boundary()) {
		    int canon_bid = bcond_.getCanonicalBoundaryId(f->boundaryId());
		    if ((canon_bid - 1)/2 == flow_dir) {
			double area = f->area();
			double pos_comp = f->centroid()[flow_dir];
			if (canon_bid - 1 == 2*flow_dir) {
			    side1_pos += area*pos_comp;
			    side1_area += area;
			} else {
			    side2_pos += area*pos_comp;
			    side2_area += area;
			}
		    }		    
		}
	    }
	}
	// delta is the average length.
	return  side2_pos/side2_area - side1_pos/side1_area;
    }
    double UpscalerBase<Traits>::computeAverageVelocity(const FlowSol& flow_solution,
                                                               const int flow_dir,
                                                               const int pdrop_dir) const
    {
	double side1_flux = 0.0;
	double side2_flux = 0.0;
	double side1_area = 0.0;
	double side2_area = 0.0;

	int num_faces = 0;
	int num_bdyfaces = 0;
	int num_side1 = 0;
	int num_side2 = 0;

	for (CellIter c = ginterf_.cellbegin(); c != ginterf_.cellend(); ++c) {
	    for (FaceIter f = c->facebegin(); f != c->faceend(); ++f) {
		++num_faces;
		if (f->boundary()) {
		    ++num_bdyfaces;
		    int canon_bid = bcond_.getCanonicalBoundaryId(f->boundaryId());
		    if ((canon_bid - 1)/2 == flow_dir) {
			double flux = flow_solution.outflux(f);
			double area = f->area();
			double norm_comp = f->normal()[flow_dir];
			// std::cout << "bid " << f->boundaryId() << "   area " << area << "   n " << norm_comp << std::endl;
			if (canon_bid - 1 == 2*flow_dir) {
			    ++num_side1;
			    if (flow_dir == pdrop_dir && flux > 0.0) {
#ifdef VERBOSE
			      std::cerr << "Flow may be in wrong direction at bid: " << f->boundaryId()<<" (canonical: "<<canon_bid
					  << ") Magnitude: " << std::fabs(flux) << std::endl;
#endif
				// OPM_THROW(std::runtime_error, "Detected outflow at entry face: " << face);
			    }
			    side1_flux += flux*norm_comp;
			    side1_area += area;
			} else {
			    assert(canon_bid - 1 == 2*flow_dir + 1);
			    ++num_side2;
			    if (flow_dir == pdrop_dir && flux < 0.0) {
#ifdef VERBOSE
				std::cerr << "Flow may be in wrong direction at bid: " << f->boundaryId()
					  << " Magnitude: " << std::fabs(flux) << std::endl;
#endif
				// OPM_THROW(std::runtime_error, "Detected inflow at exit face: " << face);
			    }
			    side2_flux += flux*norm_comp;
			    side2_area += area;
			}
		    }		    
		}
	    }
	}
// 	std::cout << "Faces: " << num_faces << "   Boundary faces: " << num_bdyfaces
// 		  << "   Side 1 faces: " << num_side1 << "   Side 2 faces: " << num_side2 << std::endl;
	// q is the average velocity.
	return 0.5*(side1_flux/side1_area + side2_flux/side2_area);
    }