In addition to SilverAzide's options, I'll add a 3rd: compute it yourself in one or two Calc measures - after all, you just have to add the current percentage to the sum of past (current) percentages, and divide it by how many times you retrieved the data (or the number of updates since you started measuring it). Personally, I prefer this rudimentary but effective approach to using AverageSize, which has one or two not so obvious drawbacks (I talked about them in the past, but can't recall what they were right now). The implementation is trivial, you can easily do it yourself. Of course, you'll only be measuring the average since the skin was loaded or refreshed.But it does not display the AVERAGE.
Here's a preview of how I measure the current (blue) and the average (orange) CPU usage of Rainmeter over an arbitrary period of time (green) in one of my skins, using the above method:
Statistics: Posted by Yincognito — Today, 1:20 am — Replies 113 — Views 204191