Page "Anemometer" Paragraph 6

The three cup anemometer developed by the Canadian John Patterson in 1926 and subsequent cup improvements by Brevoort & Joiner of the USA in 1935 led to a cupwheel design which was linear and had an error of less than 3 % up to.

Patterson found that each cup produced maximum torque when it was at 45 degrees to the wind flow.

The three cup anemometer also had a more constant torque and responded more quickly to gusts than the four cup anemometer.