Just a quick follow on regarding the meaning of "RL". It is an...

Just a quick follow on regarding the meaning of "RL". It is an acronym for Reduced Level. Best to google that term to understand what it means, but basically it is the distance between an assumed data level point measured in vertical metres.

Thus the assumed data level point is given the value of zero and thus one can refer to plus or minus RL in metres......... e.g 100RL or -100RL etc etc. The assumed data level point can be the mean sea level or something else that might be relevant to the ground or topography relative to the need or purpose.

In BRB's case the zero point or assumed data level is 300m below the surface.

Cheers