Heard a guy on a podcast say he caught it from a Bortle 8 zone with 10x50s, but he had to use averted vision and tap the binos while staring just off to the side of where he thought it was. The trick was knowing exactly where to look, like the star hop from Mirach to Mu Andromedae to Nu Andromedae, then the smudge sits just past Nu. Said it looked like a thumbprint on a dirty window, not much more. From your spot that faint gray smudge was probably the real thing, honestly. A 6 inch dob would pull it in better but a dark site trip would beat both by a mile.

What did the cheap gauge actually read, static pressure at the hood or a pressure difference between the kitchen and the rest of the building? Because those two tell you very different things (one's about the hood, the other is about the whole envelope), and I'd want to know which one he was trusting before I copied his trick. And did he say the 10 percent was measured at the hood or at the unit? I've seen guys check at the MAU and call it done, which misses leaks and duct losses completely. Two minutes per hood sounds great until you're chasing the wrong number.