The measured contact angle is calculated for a rough, heterogeneous surface using the Wenzei and Cassie laws. The contact surface is a mixture of materials A and B. With sliders, you can change the fraction of component A and the surface contact angles of each material (θ_A and θ_B). Also, a slider can change the surface roughness; for a completely smooth surface, the surface roughness ratio used in the Wenzei equation is 1. The measured contact angle (θ_W) is calculated and displayed above the water droplet graphic; arrows on the plot show where θ_W is measured. Surfaces with water contact angles θ_W > 90° have low wettability and are considered hydrophobic, whereas θ_W < 90° means the surface has high wettability and is considered hydrophilic. When θ_W = 0°, complete wetting occurs.