Maybe I don't pay enough attention, but are people really preaching that 10% of your body weight is the amount of lead that you need? Instead of what is taught (at least by PADI anyway). Which is that 10% of your body weight in lead is an estimate for a starting point in determining how much lead you'll need. The only way to truly know is to gear-up and get in the water.
Now, I'm aware of the ongoing debate about whether or not a person should have some ditchable weight. But, some people are saying that there's an actual % for determining this weight? Is this another "starting point", or are they preaching it as a hard rule or "dive law"? If they are, I'd be interested to see the formula, equation, data, variables, or whatever, that they used to determine that %.