http://www.barb.co.uk/resources/reference-documents/how-we-do-what-we-do
This is a better page to include - an actual, detailed explanation for how the data is gathered.
And again, you didn't respond to me directly, so I'll say it again - You cannot take such a tiny portion of a market (if you're even getting any data for a particular title during that week, which I highly doubt you can receive for every game out there) and balloon it out to a precise and exact number to the nearest unit and rank them. I don't care what page is added, it's impossible and the final figures appear misleading because of it. It's a matter of integrity and professionalism. It's one thing if you're covering the majority of a particular market and you can say with reasonable confidence one game sold X amount over the other, but that's not the case here.
