Showing Data on a Reversed Component

I attempted to do that when I first set up the gauges, but the component wouldn't accept a min or max value in the negative range. My path to that solution is here:

I'm not quite sure how to make a value change transformation work, because this data is being fed in live from a device that outputs from -6 to 14. The right side of my gauge correctly reads and displays the positive values like I want. Then I essentially need the left side to ignore any positive values coming in, read the negative values, then translate those into a "reverse" (ie -3 becomes 3) so that they can be displayed by the fill on the gauge.