"H"
Scales 

H 
The H scale is used in electronics
calculations for the resonant frequency of a circuit.
It is effectively a folded BI scale with the fold at 1 /
(2π). Formula: H = 1 / ( 2π² × X² ) 
H_{1} 
The H_{1} scale provides a rapid
means of calculating the square root of 1 + the square of
the value on the C scale. H_{1} runs from 0.1
to 1.0 on the C scale, and is normally located on the top or
bottom rule. Formula: H_{1} = √( 1 + X² ) 
H_{2} 
The H_{2} scale provides a rapid
means of calculating the square root of 1 + the square of
the value on the C scale. H_{2} runs from 1.0
to 10.0 on the C scale, and is normally located on the top
or bottom rule. Formula: H_{2} = √( 1 + X² ) 