The Golden Compass
"What is it?" she said.
"It's an alethiometer. It's one of only six that were ever made. Lyra, I urge to again: keep it private. It would be better if Mrs. Coulter didn't know about it. Your uncle --"
"But what does it do?"
"It tells you the truth. As for how to read it, you'll have to learn by yourself." (4.75-78)
"Yes, it might have been. Or else it might've been just in passing. Yes. I think that was it. This Scholar, I think he was from New Denmark, he was talking to the Chaplain about Dust and I was just passing and it sounded interesting so I couldn't help stopping to listen. That's what it was." (5.14)
"That's a Greek word. I reckon it's from aletheia, which means truth. It's a truth measure." (7.118)