alt Hacker NewsGenerally, other atomic clocks. The fact they they tick consistently compared to each other is the main thing (though at these scales, you need to account for time dilation!).
Generally, other atomic clocks. The fact they they tick consistently compared to each other is the main thing (though at these scales, you need to account for time dilation!).
Clocks at NIST Boulder in Colorado run faster than NIST Gaithersburg in Maryland by about 1.55 microseconds per year because of the 1500 meter altitude difference. It's about 1 nanosecond per year per meter. They both have to use a fudge factor to adjust down to sea level.