Multi-Author Ad Sharing Formula

[planeboy747]

My blog has many authors, and I am going to begin splitting ad impression inventory with them, so they earn ad revenues. Each author will be using their own Google AdSense code on their blog posts--this eliminates the need for me, the site owner, to have to manage and distribute funds.

80% of the ad impressions will go to the authors and the other 20% will go the site.

I'm in the process of having a custom Wordpress plugin developed that will bring this functionality to life. There are several wordpress plugins already, but I can't find any that work exactly like I want (or presently works because of lack of updates).

My big question is around how my blog will determine the 80/20 split. I have no familiarity with how this will be coded on the backend, and want to make sure that as I'm working with a developer that I have the proper checks and balances to ensure this is working properly. Is there some technical mathematical formula I should be referencing with my developer to ensure this is done correctly?

Thanks
J