which type of paint thickness gauge?

[jason rawls]

Ok I've done a little researching and decided that it would be safer and more professional to use a paint thickness gauge on customer's cars before I start buffing away. Is a $50 magnetic gauge going to work or am I going to have to mortgage my house and buy an electronic one?:wall

Also, what is the average thickness of the primer, base, and clearcoat altogether?

Thanks!