Seconds until the spring has settled, so a render can be sized by the motion
rather than guessed.
Found by walking the closed form rather than solving the envelope, and
the difference matters: the envelope is only an upper bound, and an
underdamped spring can sit inside it while still swinging through the target.
The honest answer is when it stops moving, not when the bound gets small.
The rest window is a whole oscillation where there is one. A single
sample near the target proves nothing — an underdamped spring passes through
it twice a cycle — but a full cycle does, because the envelope decays
monotonically, so a spring quiet for one cycle can never leave again.
Seconds until the spring has settled, so a render can be sized by the motion rather than guessed.
Found by walking the closed form rather than solving the envelope, and the difference matters: the envelope is only an upper bound, and an underdamped spring can sit inside it while still swinging through the target. The honest answer is when it stops moving, not when the bound gets small.
The rest window is a whole oscillation where there is one. A single sample near the target proves nothing — an underdamped spring passes through it twice a cycle — but a full cycle does, because the envelope decays monotonically, so a spring quiet for one cycle can never leave again.