Stats - I went to play cards in a tournament. As I watched the board with information it gave a running tally?

tally of the average number of chips each player had. At first I was a little confused on how they could know without a physical chip count and the number of players. I then realized that they could know the number of chips in the game by just taking the number of players who started the game and multiply by the number of chips each player started with. Then to calculate the average all they needed to do is divide by the number of players at any given time. This does indeed give a correct average uming no chips have left the game (ie on the floor, someone walking out with some, etc). This to me is not conventional in determining an average. If it is conventional, does it have a specific name and use. I was thinking possibly a theoretical average which could be compared to what I call a conventional average to determine relative or percentage error. Any thoughts?