A sectorial scan fires one focal law per angle, so the number of laws is (θ_end − θ_start)/Δθ + 1. The plus one is the law at the start angle. Multiply by the number of focal depths and by the number of groups configured to get the total the instrument must fire for every acquisition point.

Law count is the currency of a phased array setup. Every law consumes one pulse of the pulse repetition interval, so doubling the law count halves the frame rate and halves the scan speed at which data is still complete. A 1 degree step from 40 to 70 degrees costs 31 laws; the same sweep at 0.5 degrees costs 61 and buys very little, because the angular step is usually already much finer than the beam.

The sensible step is roughly half the beam divergence, so that adjacent laws overlap at better than −6 dB. Steps finer than that oversample the same beam and only cost time and file size.

Worked example

Start angle	-30 deg
End angle	70 deg
Angular step	1 deg
Focal depths in the law set	2
Groups configured	1
Angular span	100 deg
Laws in the sweep	101
Total laws fired per acquisition point	202
Angular remainder not covered by whole steps	0 deg

A sweep from −30° to +70° spans 100°. At a 1° step that is 100/1 = 100 intervals plus the law at the start angle, so 101 laws. With two focal depths the instrument fires 202 laws at every acquisition point.