Carlo Rovelli says sufficiently precise clocks tick differently at different heights

What was said

"If I take 2 clocks, 2 watches— this is the one I have on my wrist, and let's take this one on your table— and if they indicate the same time, okay, look, I check them, they indicate the same time. I move one of the 2 up, I wait a little bit, 1, 2, 3, 4, and then I come down and I look again. If the 2 clocks are good enough, they don't indicate the same time anymore."

Explaining relativity in practical terms, Carlo Rovelli says that if two sufficiently accurate clocks are synchronised and one is raised and lowered, they will no longer show exactly the same time. He adds the effect is tiny but measurable with very good clocks at roughly 30–40 inches of height difference.