Thank you, Greg and John.
Perhaps I get testy these days, at what I see as a complete failure of the schools to teach kids to think or even read.
"What body part do you measure from" is an absurd question, as the standard does not mention ANY body part. Rather, it discusses the height of the surface you're operating from, in relation to the area around it.
For that matter, it is irrelevant whether you are standing, sitting, laying down, or even doing a handstand.
Let's create an example to illustrate the point. Let's assume you wish to hang some holiday lights from the side of a pedestrian bridge, and are using a boom lift to extend out across the water. Do you need to wear a harness?
The answer is: as long as that basket is never raised more than 6-ft. above the water, you don't need a harness at all.
For a contrary situation, let's assume a situation where you need to remove part of the railing from a scissor lift. Now, since you don't have that railing, a harness might be required - though using a scissor lift does not usually require the use of a harness.
As for the OP's comments regarding harnesses vs. belts: one factor that applies is the type of restraint system. In most instances, a belt is adequate when an 'inertial' restraint is used, while a simple lanyard requires a harness.
Don't overlook other hazards by your blind obedience of "the rules." My employer had a man get killed (in another plant) when the lanyard got caught in the machinery. At my plant, we had a person get wrapped around a spinning shaft (broke nearly every major bone, but he's OK now) when the mandated unrolled shirt sleeve of his sturdy 'fire resistant' shirt got caught. Oops.