\begin{definition}[Definition:Imperial/Mass/Grain]
The '''grain''' is the imperial unit of mass which is used as the basis of all three of the imperial weight systems.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''grain'''
}}
{{eqn | r = \dfrac 1 {437 \cdot 5}
      | c = ounce avoirdupois
}}
{{eqn | o = \approx
      | r = 64 \cdotp 8
      | c = milligrams
}}
{{end-eqn}}
\end{definition}