Drag the point on the chart, or pick a preset load. The point is Γ in the complex plane; the chart is the Möbius map Γ = (z − 1) / (z + 1) of the normalized impedance z = Z / Z₀. Type R + jX to set the load directly, or use the line-length slider to rotate the point along a constant-|Γ| circle (the WTG behavior).