NEC then repeats this entire series of calculations while changing the signal so it approaches the antenna from different angles along the "X" and "Y" axes, storing the results for each combination of angles. The results are then normalized to the strongest signal received (almost always at "X" and "Y" = 0, or "head on") to produce a 3D pattern illustrating the relative gain for every angle. The gain relative to an isotropic antenna (dBi), front-to-back ratio, standing wave ratio and the general reception pattern are all evident from these numbers. Programs often process this into more common forms like Smith charts.