Updating after change in a property sheet (observer pattern)

Module Design
1

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.