Looks to me like you're calculating a $/file number (or cents/file by multiplying by 100). I've tracked this statistic since I began shooting stock in January, and have found that SS - due to it's vastly different business model - throws the usefulness of a global number (i.e. one that includes all sites) out the door.
That being said, I find it worthwhile to track $/file on a site-by-site basis. Sure, it's nearly meaningless for SS, but very informative everywhere else. Just so you can see what I mean, take a look at these graphs: (gray=daily values, red=7 day moving average, blue=best curve fit)
(http://www.strathdee.net/temp/income_per_file.jpg)
I could blab on and on about how I use this data, but think that I'll just wind this up by saying that, in my opinion, conjuring up a global/universal number for $/file, although interesting, has no real use in tracking portfolio performance. The only reason for tracking performance is to (attempt to) optimize it, and that's something that can only be done on a site-by-site basis.