Crystal Reports Moving Point Average

Message

     I have previously posted this problem and no solution was found - so I thought I would try again
I am using crystal v9. 
I need to chart the moving point average for a period of 15 points.
The data is pretty straight forward - ie

Sample No               Result           Moving Point Average
1                                   20                       20
2                                   28                       24 (Average of S1+S2)
3                                   10                       19 (Average of S1+S2+S3)
4                                   18                       19 (Average of S1+S2+S3+S4)
.                                     .
.                                     .
.                                     .
.                                     .
.                                     .
15                                 50                         16 (Average of S1...S15)
16                                 62                         18 (Average of S2....S16)
17                                 33                         21 (Average of S3...S17)

The data is generally only manipulated after the first 14 sets of data (ie for a 15pt average)  Then the average is only done on the last 15 data points.  I can be easily done through Excel as a trendline on the chart - surely it can also be done in crystal
Can anyone help with the code to do this and how to chart both the result and moving point average on one chart.