\begin{definition}[Definition:Angle/Unit/Second]
The '''second (of arc)''' is a measurement of plane angles, symbolized by $''$.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''second'''
}}
{{eqn | r = \dfrac 1 {60}
      | c = minute of arc (by definition)
}}
{{eqn | r = \dfrac 1 {60 \times 60} = \dfrac 1 {3600}
      | c = degree of arc
}}
{{end-eqn}}
\end{definition}