\begin{definition}[Definition:Imperial/Area/Square Inch]
The '''square inch''' is an imperial unit of area.
One '''square inch''' is equal to a square of side $1$ inch in length.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''square inch'''
}}
{{eqn | r = 6 \cdotp 4516 = 2 \cdotp 54^2
      | c = square centimetres
}}
{{end-eqn}}
The definition is exact.
\end{definition}