Totally get it. I ran an old Nikon F2 prism through one and the difference in the viewfinder was shocking.

Yeah, marywells is right, that place is a nightmare.

Wait, a chattering governor in a downtown high-rise? That sounds like a nightmare scenario. I can't imagine the noise echoing through all those floors. One call back for that and yeah, I'd be glued to a tension gauge forever too.

Man, that's just how everything is built these days, isn't it?

Smart move with the Ardex. That stuff is perfect for small dips. I've done the same thing with Henry 547. Just make sure you prime the spot first, or it can flake up later. Key is to feather the edges out real thin so you don't create a new bump. Works way better than messing with shims under the underlayment.