Trellis column charts are nice, but hard to use effectively when each chart has its own y-axis scale.  How can I set them to a common scale, or, in the case where I have both vertical and horizontal charts, set either the vertical or the horizontal charts to a common scale?  

For example, in Walkthrough 1: The Basics of Discover, the second exercise creates a set of vertical and horizontal column charts.  How would I get these to use the same y-axis scaling, either for all or for all from the same product category?