Bypassing dynamical systems : A simple way to get the box-counting dimension of the graph of the Weierstrass function

In the following, bypassing dynamical systems tools, we propose a simple means of computing the box dimension of the graph of the classical Weierstrass function defined, for any real number~$x$, by~${\cal W}(x)=\displaystyle \sum_{n=0}^{+\infty} \lambda^n\,\cos \left ( 2\, \pi\,N_b^n\,x \right)$, where~$\lambda$ and~$N_b$ are two real numbers such that~\mbox{$0 <\lambda<1$},~\mbox{$N_b\,\in\,\N$} and~$\lambda\,N_b > 1$, using a sequence a graphs that approximate the studied one.