Not the best system - Hornady Lock-N-Load Bullet Comparator Basic Set

Whidden Gunworks makes a comparator out of steel that uses standard steel neck bushings. All you have to do is resize a case with minimal neck tension, seat a bullet too long, then chamber the dummy round. This bullet can then be measured at the rifling marks left on that bullet as it's pushed back in the case. Using this measurement, you will then know the correct size bushing for the comparator so you have a meaningful way of measuring all bullets for your rifle using one number.
The Hornady system measures so far down on the ogive that a measurement must be taken for each bullet you use and because of different ogive profiles, these measurements will all be different. The Hornady products are made from aluminum which is more profitable for them but not as good for the user.