Kudos for the explanation, this is why I still come to slashdot.
I haven't spent much time looking, so this was the best I could find:
Dell also said accuracy will depend on how far away the object is. From 3 feet to 15 feet, it’s about 98 percent accurate. And from 15 feet to 20 feet its 90 to 93 percent. Beyond 20 feet, it’s too far away to be accurate at all.
The product page doesn't really make this clear at all, the only distance it ever metions is up to 30M and that's in relation to changing the focus.
I'm surprised they made it such a big feature given how limited it is. Might as well just estimate the distances yourself.