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
Cylinder set measure "γ" is the standard Gaussian measure on R. The canonical Gaussian cylinder set measure on an infinite-dimensional separable Hilbert space "H" does not correspond to a true measure on "H". The proof is quite simple: the ball of radius "r" (and center 0) has measure at most equal to that of the ball of radius "r" in an "n"-dimensional Hilbert space, and this tends to 0 as "n" tends to infinity. So the ball of radius "r" has measure 0; as the Hilbert space is a countable union of such balls it also has measure 0, which is a contradiction.