The not so palatable answer to your question is simply that you have to understand the mathematics. The 'Whiz Wheel' is nothing other than a basic table of relational values and it is intended as an 'aid memoir' and to save you the working out on paper, the mathematical solution. A circular slide rule.
If you do not understand the basic mathematical concept then the 'Whiz Wheel' is of no use to you. Sorry if that sounds hard and I realise that I am not offering you a simple solution, which is probably what you wanted but trust me here - learn the pure mathematical concept and then you will discover not only the answer to your dilemma but also in the process, an ability to do most of what you need to acceptable tolerances, in you head will become reality.
Best Wishes