Hier das Minimalbeispiel:
\documentclass[11pt,fleqn,numbers=noenddot]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[locale=DE]{siunitx}
\usepackage[ngerman]{babel}
\usepackage{multirow}
\begin{document}
\setlength{\tabcolsep}{8pt}
\renewcommand{\arraystretch}{1.5}
\begin{tabular}{|l|l|l|l|l|}
\hline
\Large{Zusatzmasse}
&
\Large{Messung}
&
\Large{$t$ in $\left[\si{\second}\right]$}
&
\Large{$\overline t$ in $\left[\si{\second}\right]$}
&
\Large{$a$ in $\left[\frac{\si{\meter}}{\si{\square\second}}\right]$}\\
\hline
\hline
\multirow{5}{*}{$1$} &$1$ &$4,4434$ &\multirow{5}{*}{$4,44628$} &\multirow{5}{*}{$???$} \\
\cline{2-5} &$2$ &$4,4388$ & & \\
\cline{2-5} &$3$ &$4,4419$ & & \\
\cline{2-5} &$4$ &$4,4416$ & & \\
\cline{2-5} &$5$ &$4,4657$ & & \\
\hline
\end{tabular}
\end{document}
