flags on palaces

i learnt a new thing last week about flags on royal palaces. i always thought it was the case that if a union jack was flying it meant the queen was in residence.
however, it’s only this standard flag here which means she’s actually in the building. the union jack is just general decoration.
apparently the queen’s standard is raised as she enters the building and lowered when she leaves to go off to one of the other palaces.
so now we know.