There are two ways elements are updated. The first is on a timer of 0.5 seconds. The second is when an element loses focus.
The global inputs are meant for things like tax and tip. This should make the cost splitter's numbers match the receipt better. The adder value is added to the subtotal and then multplied to get the total. For payment, all costs gets multiplier, and the adder is split proportionally. Try it out!