Step 1
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write down every noun you can think of related to that system. we're looking for 'measurement' type things, but anything is good. percentages and ratios are good, but try to break those down into what is being divided by what, and write those down as well.

Step 2
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cycle through your words a few times, build a few hierarchies that group them

Step 3
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cut down your list of words into things that are 'core', things that aren't 'measurements' should be reworded into measurements

Step 4
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make groups of words that you think are composites of one another, 'functions' in a way

Step 5
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pair words at random that you think are related, graph what you think their relationship looks like. estimate that graph into an actual equation.

Step 6
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trim your words down to things you have equations for, build a Computer Algebraic Model for the system you've come up with so far, run some simulations to see if it looks like what you expect