Found a nasty workaround that will work for a single story that is different to project zero story only
Start by setting Options/Project Preferences/Reference Levels, then giving '2nd reference level' as the height of your chosen story above project zero, added to sea level story (result will generally be negative if sea level is negative).
Then place spot level markers with gravity mode on, for mesh/roof/slab
AFTER spot levels is in place, select just the spot level text, click the small triangle/expander to swap default 'measured value' to 'custom', at which point a new clickable triangle/expander option appears on right hand side of dialog, in which there are some autotext options available.
Select the 'to second reference level' option, and now the intended level displays
This workaround is of no use at all if you need to do anything similar on more than one story (there is only that one user customisable reference level available) , so a proper solution still required!
PAUL KING | https://www.prime.net.nz
ArchiCAD 8-28 | Twinmotion 2024
Windoze 11 PC | Intel Core i9 10900K | Nvidia Gforce RTX 3080 | 32 Gb DDR3 | 2x4K monitor extended desktop