Anemometer trees, and both natural canyons and artificial canyons (urban buildings). The standard anemometer height in open rural terrain is 10 meters. Anemometer An anemometer is a device used for measuring wind speed, and is also a common weather station instrument. The term is derived from the Greek word "anemos", which means wind, and is used to describe any wind speed instrument used in meteorology. The first known description of an anemometer was given by Leon Battista Alberti in 1450. The anemometer has changed little since its development in the 15th century. Leon Battista Alberti (1404–1472) is said to have invented
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