can you create a sample workbook or fake data to help you?
It sounds like you may want to use a 'quick table calculation' to compare the difference of the current data point to another eg compare each day to the previous day or compare each day to the start day.
Have a look at this help document Quick Table Calculations and look at either the Difference or % Difference quick table calculations. When working with these, if you then 'edit table calculation' once applied, you should have an option to define the point you want to compare against (usually first, previous, next or last).
See how you get on. If you're still struggling, then like Deepak suggests, please provide a packaged workbook with some sample data and screenshots that help describe what you're trying to get to.
I recommend you have a read of the the Required Reading articles on the Getting Started in the Forums page to help you understand a bit more as to how to add a packaged workbook, and why we ask for one.