Relationship metrics

Hi all,
I'm not a maths guru by any means, so maybe this is something that is easy to you guys.

What I'm trying to do is work out how to build a relationship between two metrics. The first metric is something that we will be adjusting up or down to great extent with the second getting no action from us at all. What I'm trying to figure out is an equation or mathematical principle to work out how increasing the first affects the second. The two items will not necessarily be numbers, but a thing, data set or item that will have 'more of' so to speak. We need to be able to reference this over time, so historical analysis inclusion would help.

Thanks!!

This is way too imprecise. This sounds similar to describing mathematically how a friendship develops between two people. Until you do a significant work of formalizing the problem and describing it using well-defined mathematical objects, this problem is not in the scope of mathematics.