A rotating laser is being used to control the casting of a concrete floor slab. The instrument is set up over a TBM that has a reduced level of $-2\mathrm{.}213$mAOD and the projected plane is $1\mathrm{.}525m$ above this height. The base of the floor slab has a reduced level of $-3\mathrm{.}080$mAOD and the slab must be $350mm$ thick. What height on a levelling staff must the laser detector be mounted in order to ensure the slab is cast to the correct thickness $($please state the value in metres and quote the value to three decimal places$)?$