How does the banker in Deal or no Deal calculate his offers?

Question

How does the banker in Deal or no Deal calculate his offers?

Answer 1

I believe he averages what's left on the board, but then makes a decision on what to offer based on what has happened.

For example, when someone is going really well and then all of a sudden goes badly the offer will be particularly low.

When there are just 2 cases left to be opened the offer is usually the average of the 2.

Answer 2

I haven't watch the show and things may have changed, but when I did watch the show he did this:

Add up the number of unopened boxes (including the one that the player has).  This is the same as the number of prizes left on the board.  Call that number N.

Add up the sum of the prize money left up on the board.  Call that M.

M/N is the average prize per box left.  Back then, that is what he used.