Calculating The Rolling Average In Crystal Reports?

I'm trying to calculate the rolling average in a crystal report. I have got 4 weeks in a month, and I have calculated the average for each week so long. Now I want to calculate a rolling average. eg:

For week1: rolling average = (week1Average)/1
For week2: rolling average = (week1Average + week2Average)/2
For week3: rolling average = (week1Average + week2Average + week3Average)/3
etc.

The problem with the code below is that, it is not looping through,therefore the rolling average for each week is the same as its average value wich is not correct.

Dim i, weekNum as number
Dim tot as double
weekNum =Distinctcount({ItemRating.WeekNo})

[Code].....