R-value

Name	Symbol	Quantity	SI units
R-value	R	thermal insulance	(m² K)/W
The R-value, symbol R, is a non-SI unit of thermal insulance. The R-value is not accepted for use with the SI.
Definition			c² Δν_Cs^-3 k^-1
$1 \mspace{4mu} \text{R} \mspace{6mu} = \dfrac{(9 \mspace{4mu} 192 \mspace{4mu} 631 \mspace{4mu} 770)^3(1.380 \mspace{4mu} 649 \times 10^{-23})}{(299 \mspace{4mu} 792 \mspace{4mu} 458)^2} \mspace{6mu} \dfrac{c^2}{{\Delta \nu _{Cs}}^3 \mspace{4mu} k}\\ \\ \\ 1 \mspace{4mu} \text{R} \mspace{6mu} \approx 1.193 \mspace{4mu} 332 \mspace{4mu} 499 \mspace{4mu} 625 \mspace{4mu} 075 \mspace{4mu} 118 \times10^{-10} \mspace{6mu} c^2 \mspace{4mu} {\Delta \nu _{Cs}}^{-3} \mspace{4mu} k^{-1}$