"F"
Scales 

F 
The F scale is a root and power scale, used
with the fundamental scale to raise values to the 4th power,
or take the 4th root of a value. It runs in values from 1 to
10,000, and is normally located on the top rule or bottom
rule. Formula: F = X⁴ 
F(2π)  The F(2π) scale is used in electronics
calculations involving resonant frequency computations. Gauge marks are located at π and τ. Formula: F(2π) = X / ( 2π ) 
Fahrenheit 
This is a temperature conversion scale, used
with its counterpart, the Celsius scale, to convert between
degrees Fahrenheit and degrees Celsius. This scale
runs from 10 to 212 °F and is located on either the top or
bottom rule. 
FI 
The FI scale is a reciprocal root and power
scale, used with the fundamental scale to raise values to
the 4th power, or take the 4th root of a value. It runs in
values from 10,000 to 1, and is normally located on the top
or bottom rule. Formula: FI = 1 / X⁴ 