It took me a bit of time to come up with a mechanism by which such a situation could happen at all (if one leaves out parallel processing.)
In every case I have been able to think of, there has to be a callback involved (whether handle graphics or timer or serial object or the like.) Without parallel processing, callbacks are the only mechanism to (however temporarily) get a second thread going that can do independent work such as changing a variable. And if you are going to have a callback involved, one might as well wait on a graphics object property that stands proxy for the variable being changed.
For example, in various callbacks, one might have
set(0,'UserData','X71_Updated');
set(0,'UserData','Theta_Updated');
set(0,'UserData','23Skidoo_Updated');
and then at a point where you were interested in knowing that your variable had changed, you could
waitfor(0,'Userdata','23Skidoo_Updated');
