Wind speed 3 May 1999 is often quoted as the highest-recorded surface wind speed, although another figure of has also been quoted for the same tornado. Yet another number used by the Center for Severe Weather Research for that measurement is . However, speeds measured by Doppler radar are not considered official records. An anemometer is one of the tools used to measure wind speed. A device consisting of a vertical pillar and three or four concave cups, the anemometer captures the horizontal movement of air particles (wind speed). Another tool used to measure wind velocity includes a GPS combined with pitot
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