Project GREAT: General Relativity Einstein/Essen Anniversary Test
This is kind of old (goes back to 2005/7) but fascinating. This guy got 6 atomic clock. He left 3 at home and he took the other three to a weekend outing on Mt. Rainier (~1500 meters above) – along with his three kids, of course. All this to test one of most famous Einstein’s postulates. Here’s the link.. Don’t miss the family pictures section.