I'm trying to create a chart which shows the trailing 52 week total for a variable (in this example Sales). Basically, on the chart below, the value for weekname 2004/01 is the sum of that week's sales plus the previous 51 weeks' sales, for 2013/52 it is the sum of that week and the previous 51 weeks sales. I also want to restrict the view to the last 26 weeknames. The attached spreadsheet gives an example of the data and the graph I'm trying to create.
I have tried using the formula: Rangesum(Above(Total sum(Sales),0,52)) which works fine until I apply the dimension limit of using the first 26 values! I've mucked around with various options, but have now hit a brick wall.