[mehrdadn]

> We have clocks which can measure it over just a few feet of height difference

Wait, seriously? Do you have a link??

[colechristensen]

Measuring the height of a mountain with a portable atomic clock (1000m accuracy) https://www.nature.com/articles/s41567-017-0042-3

NIST measuring speed differences < 10 m/s and height < 1 m with a pair of atomic clocks https://science.sciencemag.org/content/329/5999/1630.long

[raattgift]

Tests of gravitational time dilation are also within the reach range of enthusiastic amateurs using second-hand atomic clocks:

Part 4 (starting pdf page 44) of http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_f... (slides)

Or if you prefer non-PDF:

http://leapsecond.com/great2005/

http://leapsecond.com/great2016a/

[mehrdadn]

Amazing. They observe fractional frequency changes of around 4.1E-17. Thanks for sharing the links!

[ta1234567890]

Couldn't see that number in the info at the link above, is that from the full article?

[mehrdadn]

Yeah: "The two measurements consist of approximately 100,000 s of low-height data and 40,000 s of high-height data, and the clocks exhibit (Fig. 3) a fractional frequency change of (4.1 ± 1.6) × 10^−17."