Relative growth in pivot table
 

I want to show monthly relative growth in a pivot table. Which means that
every month has to be divided by the first month entered. As well, I want to
group it by year so that the graph will display year dividers. If I don't
group it by year, the x axis will be distracting (looks like this): Jan 06
Feb 06. I would much prefer it to show the months without the year and have
year dividers.

I have used the grouping by month and year, however, the "% of" calculation
cannot compare it to the first month without getting erroneous data.

Any help would be much appreciated