Changing of the guards

[ripley]

Hi, I've read in a book that on Tower Green at The Tower of London the Changing of the guards takes place. Is that right?
I knew that the changing of the guard takes place at Buckingham and that at The tower of London takes place the cerimony of the keys.
What about the changing of the guard on Tower Green? What time does it take place? Is it similar to the Changing at Buckingham?But, primarily, does it exist as cerimony?

Thanks. Rip

[Anglika]

All military establishments that have an official guard will have a changing of the guard [up to four within the 24 hours]. It is a formal occasion and far from merely ceremonial. The departing guard will report on any unusual activity and will hand over the keys to the establishment.

Even though it is a museum, the Tower of London is still officially part of the Army.