How to convey a relation between a parameter and two things that it controls in opposite directions?

In writing the user manual for a piece of software, I'm trying to communicate the relationship between a numerical control, which I'll call frob, and two properties, which I'll call foo and bar.

Currently I have something to the effect of:

When frob is set to zero, foo and bar are unaffected by step. As frob is increased, foo increases, and bar decreases; as frob is decreased, foo decreases and bar increases.

Is there a more concise and easier to parse way to communicate this relationship to a non-technical audience?

• Define step. Are you trying to say that foo and bar are inversely related as a function of frob? Oct 12 at 2:01
• I think we need to know what the actual meanings of frob, foo, bar, and step are. Oct 12 at 4:06
• In mathematics we would often just say that "foo is an increasing function of frob and bar is a decreasing function of frob". The inverse relationship between foo and bar is then implied. Oct 12 at 12:59
• You could use something like "vice versa when it's decreased". Oct 12 at 15:42