Hammocks and Subtotals

Hello,
a hammock task is a particular task that depends on its predecessor or successor for its duration.
e.g. you want to show how long the night guard will stay in the building, from the time the last employee leaves in the evening and the first one comes the next morning.
as you do not know when they leave and come, you cannot say how long the night guard will stay; this is a perfect candidate for a hammock task.
a subtotal computes how long will be the tasks one level below it.
Alexandre

Thanks
It is more clear now.