You'll need to define expressions that set the min/max values on the Gauge - see the presentation tab. An example of this can be found in the 'Online Sales' qvw that is installed (complete install) with the product. Check the Dashboard tab of this screen and then note the behavior of the 3 gauge. There you will see that as you select values in the list bxoes that the min/max change. The expressions o nthe presentation tab for min/max hopefully give you some insight in how to set this up in your application.