\begin{definition}[Definition:Hectad]
The '''hectad''' is a derived unit of area.
One '''hectad''' is equal to a square whose side measures $10$ kilometres.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''hectad'''
}}
{{eqn | r = 100
      | c = square kilometres
}}
{{end-eqn}}
\end{definition}