$2)$ The elevation difference between points A and B have been measured by four measurements by geometric levelling technique. The observed elevation differences as well as the lengths of the levelling routes are given below:

Master St$.$ Target St$.$ Backsight Foresight Route length

$($m$)($m$)($km$)$

A $123\mathrm{.}2223\mathrm{.}202\mathrm{.}3$

$12-32\mathrm{.}31-32\mathrm{.}362\mathrm{.}8$

$2315\mathrm{.}3515\mathrm{.}391\mathrm{.}7$

$3$ B $-11\mathrm{.}53-11\mathrm{.}420\mathrm{.}9$

Compute the unit weighted rms for the average values of the backsight and foresight observations. Compute also the rms values for the average elevation differences.