Invert Channel Value

[Trickx (Tricx aka Trickx)]

Another solution is discussed here:

Changing the sign of a number coming from a thing channel

I can confirm this. I’m not familiar with JS Scripting, I suspect there’s a syntax issue there. If you tried using JRuby scripting (have to install the addon first), you can try this: |QuantityType.new(input) * -1 - I tried this and it worked. Having both fields empty will result in nothing getting updated indeed.