Creating variable including results from earlier timestep
 

I want to create a variable that will give me difference between pressure at current timestep and pressure at earlier timestep. Then I can create a contour for this variable and create an animation to show how this difference changes over time. I tried creating animation for simple pressure contour but I am not able to demonstrate the difference between timesteps because of very high scale of pressure legend. Adjusting the scale was also not useful. Does CFX have provision to do this using in-built variables it exports in results? Any pointers would be appreciated.