Replying to Measuring true center?

So maybe the answers to this thread could maybe be stickied or added to the maintenance thread but I've been unable to find this info elsewhere on ns.......essentially measuring true center on a symmetrical ski is a no brainer but what about a rockered ski?....or a rockered ski that is asymmetrical?....I'm curious as to if I'm doing it right by measuring off of actual running surface....can anyone provide a legit explanation?