\begin{block}{The 68-95-99.7\% rule}
For every normal distribution with mean $\mu$ and standard deviation $\sigma$ holds that
\begin{itemize} \item approx. 68\% of the measurements will lie within one standard deviation from the mean
\item approx. 95\% of the measurements will lie within two standard deviations from the mean
\item approx. 99.7\% of the measurements will lie within three standard deviations from the mean
\end{itemize}
\end{block}