Anemometer Lind was not the first it was the most practical and best known anemometer of this type. If the wind blows into the mouth of a tube it causes an increase of pressure on one side of the manometer. The wind over the open end of a vertical tube causes little change in pressure on the other side of the manometer. The resulting elevation difference in the two legs of the U tube is an indication of the wind speed. However, an accurate measurement requires that the wind speed be directly into the open end of the tube; small departures
Complete measure Naïvely, we would take the "σ"-algebra on R to be "B" ⊗ "B", the smallest "σ"-algebra containing all measurable "rectangles" "A" × "A" for "A" ∈ "B". While this approach does define a measure space, it has a flaw. Since every singleton set has one-dimensional Lebesgue measure zero, for "any" subset "A" of R. However, suppose that "A" is a non-measurable subset of the real line, such as the Vitali set. Then the "λ"-measure of {0} × "A" is not defined, but and this larger set does have "λ"-measure zero. So, this "two-dimensional Lebesgue measure" as just defined is not