Quantum_clock#More_accurate_experimental_clocks: https://en.wikipedia.org/wiki/Quantum_clock#More_accurate_ex...

> In 2015 JILA evaluated the absolute frequency uncertainty of their latest strontium-87 optical lattice clock at 2.1 × 10−18, which corresponds to a measurable gravitational time dilation for an elevation change of 2 cm (0.79 in) on planet Earth that according to JILA/NIST Fellow Jun Ye is "getting really close to being useful for relativistic geodesy".

AFAIU, this type of geodesy isn't possible with 'normal' time structs. Are nanoseconds enough?

"[Python-Dev] PEP 564: Add new time functions with nanosecond resolution" https://mail.python.org/pipermail/python-dev/2017-October/14...