Anemometer use is constructed from a ping-pong ball attached to a string. When the wind blows horizontally, it presses on and moves the ball; because ping-pong balls are very lightweight, they move easily in light winds. Measuring the angle between the string-ball apparatus and the vertical gives an estimate of the wind speed. This type of anemometer is mostly used for middle-school level instruction, which most students make on their own, but a similar device was also flown on Phoenix Mars Lander. The first designs of anemometers that measure the pressure were divided into plate and tube classes. These are the
Lebesgue measure not have some curious properties which causes a discrepancy in the measure of another set when formula_6 is used as a "mask" to "clip" that set, hinting at the existence of sets for which the Lebesgue outer measure does not give the Lebesgue measure. (Such sets are, in fact, not Lebesgue-measurable.) The Lebesgue measure on R has the following properties: All the above may be succinctly summarized as follows: The Lebesgue measure also has the property of being "σ"-finite. A subset of R is a "null set" if, for every ε > 0, it can be covered with countably many