altimeeter

An altimeeter is a hypothetical instrument designed to measure time intervals with extreme precision by integrating multiple time-keeping references and direct time-transfer techniques. The term is not part of standard metrology and is mainly used in speculative discussions or fictional settings to denote an ideal time-measuring device.

Conceptually, an altimeeter would combine a primary frequency standard (such as an optical atomic clock), a supplementary oscillator for short-term stability (for example a cryogenic sapphire oscillator), and a time-interval measurement engine that computes elapsed time from phase and frequency data. It would include a time-transfer subsystem to compare its clock with remote references, using methods like optical fiber links or satellite-based time transfer.

Operation would entail continuous synchronization to a reference frame, active error cancellation for environmental effects, and robust uncertainty estimation. Calibration would rely on traceability to international atomic time scales and cross-checks against multiple standards to mitigate drift and systematic biases.

In modern metrology, real devices achieving comparable performance include optical lattice clocks and advanced atomic clocks, together with high-precision time-transfer networks. The altimeeter serves as a conceptual benchmark for what a fully integrated, ultra-stable timekeeping system might achieve.

See also: atomic clock, timekeeping, chronometer, time transfer, metrology.