I created a graphic which showes the relative time (compared two the whole working time) was used during a year.
As a final result, I'd like to see as a graphic the delta between these two years, so relative result of a product in 2011 - same product for 2010. Or to say it very easy, the result of the subtraction of corresponding colours.
Important additional information:
1) the values to which they are related (total time per year is not a constant !) but a given value in a table
2) the sum of the times used for the different products does not equal the total working time over the corresponding year.
Can this be done in the graphic itself, or should a virtual table be created to solve this issue.