Editing Hafele–Keating experiment (section)

== Similar experiments with atomic clocks==
Measurements in which the only effect was gravitational have been conducted by Iijima et al. between 1975 and 1977. They carried a commercial cesium clock back and forth from the [[National Astronomical Observatory of Japan]] in [[Mitaka, Tokyo|Mitaka]], at {{convert|58|m|abbr=on}} above sea level, to [[Mount Norikura|Norikura corona station]], at {{convert|2876|m|abbr=on}} above sea level, corresponding to an altitude difference of {{convert|2818|m|abbr=on}}. During the times when the clock stayed at Mitaka, it was compared with another cesium clock. The measured change in rate was (29±1.5)×10<sup>−14</sup>, consistent with the result of 30.7×10<sup>−14</sup> predicted by general relativity.<ref>{{Cite journal|author1=Iijima, S. |author2=Fujiwara, K. |author3=H. Kobayashi |author4=T. Kato |title=An experiment for the potential blue shift at the Norikura Corona Station|journal=Annals of the Tokyo Astronomical Observatory|year=1978|volume=17|pages=68–78|bibcode=1978AnTok..17...68I}}</ref>

In 1976, Briatore and Leschiutta compared the rates of two cesium clocks, one in [[Turin]] {{convert|250|m|abbr=on}} above sea level, the other at [[Plateau Rosa]] {{convert|3500|m|abbr=on}} above sea level. The comparison was conducted by evaluating the arrival times of [[Very high frequency|VHF]] television synchronization pulses and of a [[LORAN]]-C chain. The predicted difference was 30.6&nbsp;ns/d. Using two different operating criteria, they found differences of 33.8±6.8&nbsp;ns/d and 36.5±5.8&nbsp;ns/d, respectively, in agreement with general relativity.<ref>{{Cite journal|author1=Briatore, L. |author2=Leschiutta, S. |title= Evidence for the earth gravitational shift by direct atomic-time-scale comparison|journal=[[Il Nuovo Cimento B]]|volume=37|issue=2|pages=219–231|year=1977|doi=10.1007/BF02726320|bibcode = 1977NCimB..37..219B |s2cid=124043777 }}</ref> Environmental factors were controlled far more precisely than in the Iijima experiment, in which many complicated corrections had to be applied.{{citation needed|date=June 2017}}

In 2005, van Baak measured the gravitational time dilation of a weekend at 5400' ASL on [[Mount Rainier]] using two ensembles of three HP&nbsp;5071A cesium beam clocks.<ref>{{cite magazine |title=Amateur Time Hackers Play With Atomic Clocks at Home |first=Quinn |last=Norton |magazine=[[Wired (magazine)|Wired]] |date=12 November 2007 |url=https://www.wired.com/2007/12/time-hackers/}}</ref><ref>{{cite conference |conference=38th Annual Precise Time and Time Interval Meeting 2006 |conference-url=http://tycho.usno.navy.mil/ptti/ptti2006.html |date=6 December 2006 |first=Tom |last=van Baak |title=Project GREAT: General Relativity Einstein/Essen Anniversary Test |type=Conference presentation |url=http://leapsecond.com/ptti2006/tvb-project-great-ptti-ppt.pdf}}<!-- This ref primarily for notability: recognition by a professional society.--></ref><ref>{{cite web|url=http://leapsecond.com/great2005/|title=Project GREAT: General Relativity Einstein/Essen Anniversary Test|last=van Baak|first=Tom|date=25 September 2005|access-date=2017-03-30|quote=It was the best extra 22 nanoseconds I've ever spent with the kids.}}<!--This ref self-published, but very informative--></ref>  He repeated the experiment in 2016 on [[Mount Lemmon]] for the television show ''[[Genius by Stephen Hawking]]''.<ref>{{cite web |first=Tom |last=van Baak |title=Project GREAT 2016a &mdash; Hawking, Einstein, and Time Dilation on Mt Lemmon |url=http://www.leapsecond.com/great2016a |date=17 May 2016 |access-date=2017-03-30}}</ref>

In 2010, Chou et al. performed tests in which both gravitational and velocity effects were measured at  velocities and gravitational potentials much smaller than those used in the mountain-valley experiments of the 1970s. It was possible to confirm velocity time dilation at the 10<sup>−16</sup> level at speeds below 36&nbsp;km/h. Also, gravitational time dilation was measured from a difference in elevation between two clocks of only {{convert|33|cm|abbr=on}}.<ref>Nontechnical explanation at http://www.scientificamerican.com/article.cfm?id=time-dilation</ref><ref>{{cite journal|author1=Chou, C. W. |author2=Hume, D. B. |author3=Rosenband, T. |author4=Wineland, D. J. |author-link4=David J. Wineland | year=2010 | title=Optical Clocks and Relativity | journal=Science | volume=329 | issue=5999 |  pages=1630–1633 | doi=10.1126/science.1192720 |bibcode=2010Sci...329.1630C | pmid=20929843 |s2cid=206527813 | url=http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=905055 |url-access=subscription }}</ref>

Presently both gravitational and velocity effects are routinely incorporated, for example, into the calculations used for the [[GPS|Global Positioning System]].<ref>{{Cite conference |last=Deines |first=S.D. |year=1992 |title=Uncompensated relativity effects for a ground-based GPSA receiver |url=https://ieeexplore.ieee.org/document/185812 |conference=IEEE PLANS 92 Position Location and Navigation Symposium |publisher=IEEE |pages=7–11 |doi=10.1109/PLANS.1992.185812 |isbn=978-0-7803-0468-0|url-access=subscription }}</ref>