Updating after change in a property sheet (observer pattern)

I’d like my figure counters to display visually an indication when they’re “DEAD” whenever their ST value is less than 2. The ST value is defined and modified in a property sheet, e.g., by clicking on the tick marks for the figure’s ST.

Is there a way so that Property Sheet changes can trigger some command to “update” a text label? :confused:

I guess I’m looking for something like the “observer” design pattern (subscriber to a change), but at the level of trigger actions or something.