Reconstruction of quantities for UCT1 (left) and UCT2 (right). Quantities in blue are defined at cell faces in x and y and quantities in red at the cell edge in z. The resulting line integral of the electric field ℰ_z over the edge is shown in green. Continuous arrows represent limited reconstructions (steps 2 and 3 of UCT1, and 3 of UCT2) and dashed lines the choice of the maximum value (step 5 of UCT1 and 4 of UCT2, the labels L and R for the characteristic speeds are omitted in the figure to avoid saturation). The average transverse transport velocities needed in UCT2 (step 2) are computed using the quantities in the boxes.