Davis Windex Wind Direction Indicators Windex provides the helmsman with accurate information of the apparent wind direction. The balanced vane has low inertia, a large fin area, low-friction suspension and responds quickly and accurately at wind speeds as low as 2/10 knots. Windex is tested in wind tunnels at speeds up to 80 knots and has proven its mechanical ruggedness. Masthead mount. Vane length 15".