$4\mathrm{.}18$ In trigonometric leveling from point $A$ to point $B,$ the slope distance and zenit angle measured at A were $2504\mathrm{.}897m$ and $85{08}^{\text{'}}{54}^{\text{'}\text{'}}.$ At $B$ these measurements wer $2504\mathrm{.}891m$ and $94{52}^{\text{'}}{10}^{\text{'}\text{'}}$ respectively. If the instrument and rod target heights wer equal. calculate the difference in elevation from $A$ to $B.$