Memory window = 4. For each call: messages the model received, messages stored at that moment, messages stored afterwards.
call 1: model received 1, stored 1, stored afterwards 2
call 2: model received 3, stored 3, stored afterwards 4
call 3: model received 5, stored 4, stored afterwards 4
call 4: model received 5, stored 4, stored afterwards 4
call 5: model received 5, stored 4, stored afterwards 4

Largest number of messages the memory object held after any add, used on its own: 4