\begin{definition}[Definition:Hectare]
The '''hectare''' is a derived unit of area.
One '''hectare''' is equal to a square whose side measures $100$ metres.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''hectare'''
}}
{{eqn | r = 100
      | c = ares
}}
{{eqn | r = 10 \, 000
      | c = square metres
}}
{{eqn | o = \approx
      | r = 0.4
      | c = acres
}}
{{end-eqn}}
\end{definition}