\begin{equation} \Delta(t) =\frac{\partial O}{\partial S} \end{equation}

\begin{equation} \Delta(t) =\frac{\partial O}{\partial S} \tag{1} \end{equation}

$O(t)$

$\displaystyle\frac{\partial O}{\partial S}\in(0,1]$

$\partial O / \partial S$