\begin{definition}[Definition:Imperial/Length/Inch]
The '''inch''' is an imperial unit of length.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''inch'''
}}
{{eqn | r = 2 \cdotp 54
      | c = centimetres
}}
{{eqn | r = 0 \cdotp 0254
      | c = metres
}}
{{end-eqn}}
This definition is exact, and is how the imperial unit of length is defined.
\end{definition}