Every clock counts oscillations of something and multiplies by the oscillator's known period. A pendulum's period depends on its length and local gravity — both nudged by temperature, humidity, air pressure and wear, so its rate wanders by roughly 10⁻⁴ of itself from hour to hour. A quartz crystal is a far more stable mechanical resonator (roughly 10⁻⁶) but still ages and drifts with temperature. A cesium atom's hyperfine transition frequency is a fixed property of the atom itself, reproducible to about 10⁻¹³ — which is why the SI second has been defined since 1967 as exactly 9,192,631,770 periods of that transition.
accumulated error ≈ |rate offset| × elapsed time
pendulum: ~1e-4 → seconds of error per day
quartz: ~1e-6 → seconds of error per month
atomic: ~1e-13 → microseconds of error per decade
- Time speed — how many simulated days pass per real second; push it up to fast-forward through months or years.
- Run / Reset — pause the fast-forward or zero all three clocks and start over.
- Each clock's rate offset wanders slightly frame to frame (a random walk), mimicking real thermal and mechanical noise — the atomic clock's wander is scaled down by the same ~10⁹ factor that makes it useful as a time standard.
Real-world relevance: GPS, financial trading timestamps, and the internet's NTP/PTP time servers all ultimately trace back to a small number of cesium and rubidium atomic clocks precisely because a mechanical or quartz reference would drift the whole system out of sync within days to months.