Anemometer mounted on a vertical shaft. The air flow past the cups in any horizontal direction turned the shaft at a rate that was roughly proportional to the wind speed. Therefore, counting the turns of the shaft over a set time interval produced a value proportional to the average wind speed for a wide range of speeds. It is also called a rotational anemometer. On an anemometer with four cups, it is easy to see that since the cups are arranged symmetrically on the end of the arms, the wind always has the hollow of one cup presented to it and
Convergence in measure formula_14, "μ" be Lebesgue measure, and "f" the constant function with value zero. (The first five terms of which are formula_19) converges to "0" globally in measure; but for no "x" does "f(x)" converge to zero. Hence "(f)" fails to converge to "f" almost everywhere. There is a topology, called the topology of (local) convergence in measure, on the collection of measurable functions from "X" such that local convergence in measure corresponds to convergence on that topology. This topology is defined by the family of pseudometrics where In general, one may restrict oneself to some subfamily of sets "F" (instead