\begin{eqnarray*}
        P(e_t) & = & \frac{number\:events\:at\:time\:t \pm (n \ast l)\:sec}{number\:of\:recorded\:days}\\
        & = & \frac{\sum_{i=1}^D{e_{i_{t \pm (n \ast l)}}}}{D}
\end{eqnarray*}