It will be automatically called only when the values other (observables) are changed -- those on which it depends. In order to force the recalculation of an observable, one should use variableName.DB.update()
See compute.js
due= ← right after the web page is loaded, here must be the (initially defined in compute.js) value zzz, and only later, after we update uno, it should change into the value of uno repeated twice.