Gents: Don’t get too upset what people call it. We will decide here, and than it becomes the commandment the Lord hands to the prophet. The domain_id will tell everybody what we (Lord, prophet) think it is.
But we need a set of rules we like, we can put down in the description, and then use for domain assignments.
@wstephens: I agree with @bailey on the weight/height thing. Of course, you can slowly drift further to the right: Pulse (still measurement? No instrument but your iPhone), reflexes (needs a hammer, but subjective “measurement”), auskultation, Karnofsky? So, no matter where you draw the line, there will be wishy washy cases straddling it.