Max/Min as Variables

For my use, min/max need to be defined in a variety of panels. Its important for me to display the real values, but to visualize the percentage. So, for instance, 0-500 – 500 the max. For each system, and I’m looking at a hundred or so, this will be slightly different, but, is easily queried from a DB.

Is it not possible to assign a variable to the Field Max? Does anyone know a way around this limitation?