Hello everyone. Hoping someone can shine some light.

I have a given event that happen over time. The event happens to be a specific individual accessing a specific resource on an intranet. Below lists some sample data listing the day the even happens.

08/03/12

08/03/12

08/03/12

08/01/12

07/31/12

07/31/12

07/31/12

07/31/12

07/31/12

07/31/12

07/30/12

07/30/12

07/30/12

07/30/12

07/30/12

I have a formula to compute the user-resource rank (r). T is the time for the rank being calculated (08/03/12) and T0 is the first data point (07/30/12). I show it as days, but some other definition of time would work.

r=SUM from t=T0 to T (1/ (1+(T-t)))

Given the above data, the rank equals 5.8333.

So today (08/08/2012), I get a hit by the person in question. I wish to calculate his new score. If I had all the old data, I could use the same formula with just one more data point. But I don't want to store the entire past history of each individual, and just want to score the last known score from the individual (5.8333) and the date it was calculated (08/03/2012). I would then depreciate this last score based on the duration from today and when it was created (5 days) and then increment it for the latest hit.

It's the depreciation part that's got me stumped. Intuitively, I would think this would be possible, but am not sure. If not possible, maybe some approximation?

Thank you in advance for any suggestions or advice.