Magnets

Is there any way I can measure the power of a magent using a more precise method than my own judgement?

If not, are there classes of magnets? I'm just thinking, once I get club racing, I'll probably want a bit more or less magnet. Is there any way to do this without trial and error?

Example:

Fly magent is too strong, but I don't want to be sliding all over the place. I want a magent less powerful than a fly but more than say, a ninco.

Just an example of course, but I hope you get the idea.

Thanks.