reciprocal metre

Name	Symbol	Quantity	Base units
reciprocal metre	m^-1	wave number	m^-1
The reciprocal metre, symbol m^-1, is the SI coherent derived unit of wavenumber. One reciprocal metre is equal to one divided by one metre.
Definition			c^-1 Δν_Cs
$1 \mspace{4mu} \text{m}^{-1} \mspace{6mu} = \dfrac{299 \mspace{4mu} 792 \mspace{4mu} 458}{9 \mspace{4mu} 192 \mspace{4mu} 631 \mspace{4mu} 770} \mspace{6mu} \dfrac{\Delta \nu _{Cs}}{c}\\ \\ \\ 1 \mspace{4mu} \text{m}^{-1} \mspace{6mu} \approx 3.261 \mspace{4mu} 225 \mspace{4mu} 571 \mspace{4mu} 749 \mspace{4mu} 405 \mspace{4mu} 557 \times10^{-2} \mspace{6mu} c^{-1} \mspace{4mu} \Delta \nu _{Cs}$

The reciprocal metre is used in optics as a measure of the optical power of a lens or curved mirror.