Rating system for online games in Heroes of Might and Magic IV.

Do you think this is optimal? :)
Let's say my rating is 100, and I missed only one game:
100-1/2=99.5 - is this rational from that perspective?

Do you think people will immediately try to attend a game because of a 0.5 rating difference? I think it needs to be more balanced.

Hmm... and you can make it more strict either by not dividing at all or by multiplying as well. He simply took up an unnecessary place in the table, and he will be penalized for this by deducting points. But in what quantity...
Rnew=Rold-N/2 or Rnew=Rold-N or Rnew=Rold-N*k, where k is a coefficient.
What do you think?