The figure on the right shows the top left-hand corner of the complete diagram. Note the symmetry which leads to the three measurements of

\frac{1}{2}

. Thus the diagonal of the square can be divided into three portions of lengths:

$\frac{1}{2}$ , $x$ and $\frac{1}{2}$ respectively.

The length of the diagonal $= \sqrt{10^{2} + 10^{2}} = \sqrt{200} = 10 \sqrt{2}$ .

So $x$ = $10 \sqrt{2} - 1$ .