This morning, Nora gave out a high-pitched mew. Lis said, "I wonder what note that was?" I thought about it, and said, "G over high C."
Then I wondered if I was right, so googled around for someone playing a G over high C, played it, and I was spot-on -- that was EXACTLY the note.
I don't have perfect pitch, but I try to carry middle C around with me, and then I can work off of that to figure out other notes. And it worked.