Relational Duration from Finite Physical Records

Duration can be reconstructed from finite physical records through the dynamics and calibration of internal clocks. Finite classical, relativistic, and stationary quantum models show how the available records and clock interactions affect this reconstruction. For a prepared oscillator, exact optimal error bounds identify when adding a record combining position and momentum improves the duration estimate, while a coupled pointer provides a consistency test for sampled readings. Separatrix passage, Sagnac returns, and quantum backflow illustrate the construction across these settings. The calibrated predictions agree with conventional descriptions without an independently supplied time interval.