Measure option in the definition of a dimension

Hello

I have SW 2019 SP 5.0 as well as a memory gap. I can't remember how the Measure option works in the dimension editing window, options offered after entering the = sign instead of a numerical value. This option is only available when editing a part in the context of an assembly (for a single part it is only proposed Function and File Properties (among which the components of the inertia matrix ... why them and not something else????)).

I am attaching an illustration to better understand.

Thank you  and have a good day to all

Stone


option_mesurer.pdf