 They always did that. Same thing with sinks, like kitchen sinks that are cast iron. I've seen the dates sort of actually cast right into those sinks. So that's one way to do it. Secondly is, of course, noticing what kind of building materials are being used here. For example, if it's copper plumbing, that's probably from the 60s. If you have old knob and tube wiring, first of all, you shouldn't still have it because it's pretty dangerous, but that's going to be from like 1900, 1910.