In levelling between two points $A$ and $B$ on the opposite banks of a river, the readings are taken by setting the instrument both at $A$ and $B$ , as shown in the table. If the $RL$ of $A$ is $150.000 \mathrm{m}$ , the $RL$ of $B$ (in $\mathrm{m}$) is $\_\_\_\_\_$ (rounded off to $3$ decimal places).
| Level Position |
Staff readings |
| $A$ |
$B$ |
| $A$ |
$1.800$ |
$1.350$ |
| $B$ |
$1.450$ |
$0.950$ |
