Excel uses only an IF statement. I have used it in an unrelated large
scale water flow situation, but found it messy to use. I was thinking
that a series of them could be used to end up with a yes (OK) or no
answer, but I like your concept better of showing where you are on the
actual CG/GW range.

In addition you could show the effect of burning off fuel as a line.
I don't think any 172s will present a problem in this area, but some
others like Bonanzas can.

My experience is that it is hard to exceed the CG range of a 172, but
easy to exceed the gross weight.