F scale

The terms F scale and F number may refer to several things:

The F-scale is a personality test that attempts to quantify authoritarian tendencies.
The Fujita scale, sometimes abbreviated "F scale", rates a tornado's intensity by its impact on structures and vegetation. Often, when a tornado is rated on this scale, it is said to have been given an "F number".
In photography, the f-number refers to the relative aperture of a lens.
The F scale is a 2.781 in (70.64 mm) gauge track used with model trains.
In chemistry, the F number is a number that can be calculated for polycyclic aromatic hydrocarbons from their structure. It is used in liquid chromatography.

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