\documentclass[a4paper,10pt]{scrartcl}

\input{Base.tex}

\begin{document}
\begin{figure}[ht]
\centering
\begin{tikzpicture}[x=1cm,y=1cm]

\def\xmax{20.8};
\def\ymax{29.5};
\def\yspace{0.25};
\def\mycolor{light-gray};

\pgfmathtruncatemacro\repY{\ymax/\yspace}

\foreach \y in {0,...,\repY}{
  \draw[\mycolor, line width=0.1pt] (0,{\yspace*\y}) -- (\xmax,{\yspace*\y});
}

\draw[\mycolor, line width=0.5pt] (0,{\ymax/2}) -- (\xmax,{\ymax/2});

\draw[\mycolor, line width=0.1pt] (0,0)           -- (0,\ymax);
\draw[\mycolor, line width=0.5pt] ({\xmax/4},0)   -- ({\xmax/4},\ymax);
\draw[\mycolor, line width=0.5pt] ({\xmax/2},0)   -- ({\xmax/2},\ymax);
\draw[\mycolor, line width=0.5pt] ({3*\xmax/4},0) -- ({3*\xmax/4},\ymax);
\draw[\mycolor, line width=0.1pt] ({\xmax},0)     -- ({\xmax},\ymax);

\end{tikzpicture}
\end{figure}
\end{document}