How Can I calculate percentage Change in Graph?

[#1]

Hi community, 

I have a line graph with values of a field on various dates.  How can I calculate the percentage change on the dates from the previous date instead?  The dates are the month.  Example:  I have a value of 500 for the stock in march and 600 in april.  I want the percentage change of 600-500/500 or 20% for April in the line graph rather than 600.

Any ideas?

[swuehl · Accepted solution]

Try something like

=sum(Stock)/above(sum(Stock)) -1

i.e. reference the expression value in the context of the previous dimension value using above() function.