First Filter.
You're welcome, Wes. I'll click on the links for filters. That should find it.
It's easier in crowded places. It ain't the same as no one being there is the thing. It's a strongly felt absence. Negative spot. Still, the more people around, the more it stands out. That's why it's easier going on the same level than up and down. That or cause I've got more practice that way. I'd guess about a city block, but I'm going to push it as much as I can.
It doesn't matter which way I'm looking. I feel it, and I know where it is.