The SI second is defined as exactly 9,192,631,770 periods of the microwave radiation that drives the hyperfine transition between the two ground-state sublevels (F=3 and F=4) of a cesium-133 atom. This scene renders that atom in a microwave cavity: its state amplitude oscillates between the two hyperfine shells (blue F=3, red F=4) in step with the driving field, and every real oscillation increments the counter. The real frequency is ~9.19 GHz — far too fast to watch — so the count speed slider compresses time so you can see the number climb toward the defining constant and watch a "tick" (one atomic second) complete.
- Count speed — how many (simulated) oscillations are counted per real second; higher speed reaches 9,192,631,770 sooner, exactly like fast-forwarding the real 9.19 GHz signal.
- Microwave detuning Δf — a real cesium clock only counts correctly when the microwave source sits exactly on the 9,192,631,770 Hz resonance; drift away from resonance drops the "lock" quality and slows/corrupts the counted rate, which is why real clocks continuously servo the microwave frequency to the atom's own transition.
- Comparison clock drift — a mechanical/quartz clock has no absolute physical reference; it just runs at a rate that can drift by parts-per-million. Sync Both Clocks zeroes both counters so you can watch them diverge in real time — the entire reason metrology replaced pendulums and quartz with the cesium standard in 1967.
1 SI second ≡ 9,192,631,770 periods of the Cs-133
ground-state hyperfine transition (unperturbed, at rest)