+To illustrate, the \emph{scan diameter} can be defined as
+\latexonly{$$s_d = s_r v_r p_d$$}\latexignore{\\$$Sd = Sr x Vr x Pd$$\\}
+
+Further, $f$ can be defined as
+\latexonly{$$f = f_r (v_r p_d / 2)$$}
+Plugging these equations into
+\latexignore{the above equation,}\latexonly{equation~\ref{alphacalc},}
+We have,
+\latexonly{
+\begin{eqnarray}
+\alpha &= 2\,\sin^{-1} \frac{s_r v_r p_d / 2}{f_r v_r (p_d / 2)} \nonumber \\
+&= 2\,\sin^{-1} (s_r / f_r)
+\end{eqnarray}
+}
+
+Since in normal scanning $s_r = 1$, $\alpha$ depends only upon the \emph{focal length ratio}.
+