Comparison of the two slab solutions for short times. What error is made by using Eq$.11\mathrm{.}5-10($based on semi$-$infinite slab$)$ instead of Eq$.11\mathrm{.}5-38($based on the slab of finite thickness$),$ when at$/$b $0\mathrm{.}1$ and for a position $0\mathrm{.}9$ of the way from the midplane to the slab surface? Using the graphically presented solution $($Figure $11\mathrm{.}5-1)$ for making the comparison.