How to plot the difference between two polled values

Hi,

I'm looking to graph/chart a value (sum, difference, etc) derived from two or more values polled from interfaces/nodes. Is it possible to generate such a value using the provided charts/graphs shipped with Solarwinds NPM or do we need to write a custom script?

If a custom script is required, whats the best way to approach that? (I prefer to work in python)

Any assistance is greatly appreciated.

Thanks