Optical illusion for sure. The boards were flat and tied in nicely.
I ended up renting a drum sander afterwards, then an edging sander, then a crappy orbital sander, then a polisher (with screen). After a ton of sanding and sweeping and tacking and such, put 3 coats of finish down...
Little history: Pulled carpet from a room that had continuous carpet installed for well over 15 years. When we pulled it, we looked at the hardwood and thought it would be great to keep the hardwood.
There was a section of floor that had been removed for a floor vent, but the vent had been...