Anemometer 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 the first mechanical anemometer around 1450. In following centuries, numerous others, including Robert Hooke (1635–1703), developed their own versions, with some
Signed measure finite signed measure is given by for all "A" in Σ. This signed measure takes only finite values. To allow it to take +∞ as a value, one needs to replace the assumption about "f" being absolutely integrable with the more relaxed condition where "f"("x") = max(−"f"("x"), 0) is the negative part of "f". What follows are two results which will imply that an extended signed measure is the difference of two nonnegative measures, and a finite signed measure is the difference of two finite non-negative measures. The Hahn decomposition theorem states that given a signed measure μ, there exist