It's like all of the other charts they've posted. There's a raw points scale (#1 worth the most, #200 the least), with the point values adjusted based on chart rules/longevity trends at the time.
So, it takes into account position and longevity, but it adjusts both. So an album that spent 2349 weeks in the Top 100 in the 1990s is going to be lower than an album with the same chart run in 2010.
