Almost. Think of it like a bank account. You don't sum up every transaction amount across all time. Instead, to calculate your balance you start from the last s

Almost. Think of it like a bank account. You don't sum up every transaction amount across all time. Instead, to calculate your balance you start from the last statement balance (the last memento according to Greg Young) and apply newer events. So it's VERY fast. You can even compute and save your newer balance (memento) every few events if you'd like.