Story is:

1. I wan to force calculation for a calculated item right after one (or a few - preferably configurable) of items in the formula got a new value.
So it should be kind of dependent to a master item.
It could be implemented that update interval settings gets a new option - update after another item got an update. And there we could select one or a few items.

2. Similar thing but from another point of view:
Allow dependent items to do calculation from more than one source item.
Not sure how that could be implemented, need to think about it more.