I was lucky enough to win tickets to a NIN concert from a radio station call-in in the late 1990's or early 2000's (it was around the time the "God is dead and no one cares" song was all the rage). These tickets included access to the soundcheck. I went and saw Trent Reznor with a walkie-talkie going seat-to-seat-to-seat in the venue (and this was a 6k+ seat venue, not counting standing-only areas which he visited as well). At each seat he would have his audio techs play ~15 seconds of a test track (i think it was the Dolby sound samples) and then radio in and have his crew adjust whatever sounded off to him then immediately move on to the next seat. Quite some time later I saw Bono from U2 getting some press for doing the same thing at his shows and always wondered if he learned that from Nine Inch Nails. That show was fucking bonkers too, NIN had a really cool light/laser show going on during the show.
Well, I was at the soundcheck in the morning (not super early, if memory serves me, this was a while ago). The concert was that evening. And yea, he was doing each seat individually, at least while I was hovering around watching everything. I can't say what he did before I got there, but yea for the 3 hours or so that I can remember he was doing each seat. I'm sure he skipped a few rows here and there, he would have to just because of time. Also, it was probably less than 15 seconds of the test track, I'm most likely exaggerating that fact subconsciously because it's a fond memory of mine.