Thank you all for your considered inputs.
Dublinpilot - Brilliant !!! why didn't I think of that !!! Easier to fill up than drain down. Award yourself a pint of Guiness ( preferably from Dirty Nellie's near Shannon Airport, circa 1960 during 707 conversion ! )
Rod1
PS this is a general comment and not aimed at you ExSp33db1rd.
Rod1 - understood, and I totally agree, even two pilots 'dipping' in the hangar with the same dipstick will come up with two different answers. In practice the difference is not very significant under normal circumstances, but that's not the point.