Long SNUADC recordings with no correction at all¶

1,066 cases of 2.5 h or longer show no SNUADC correction, although at the step-mode median of −63 ppm a 0.49 s step falls due within about 2.2 h. Slower units, a third recorder mode, or both; shared bursts point to slower units (about −36 ppm where the BIS rate is known, The stamp sawtooth model for SNUADC and BIS, due only after about 3.8 h). The Solar8000 route cannot settle it: its rates shrink toward zero in recordings under about 4 h (The SNUADC clock through the Solar8000 numerics, whole release).


Status	open: seen, not explained.
Devices	SNUADC

What it means¶

Step-mode files with no reset can carry up to about 0.4 s of drift that the stamps do not show. The first stamp model gave them a rate of 0; the adopted one (model3) gives them their port's step-mode rate, which leaves a spread of about −135 to +122 ms/h (p10–p90) because each recording drifts at its own rate (The stamp sawtooth model for SNUADC and BIS).

Evidence¶

Study	Date	Status	Summary
The SNUADC clock through the Solar8000 numerics, whole release	2026-10-19	current	On the SNUADC's own sample count, the delay from the waveform to the PC-stamped Solar8000 heart rate and mean arterial pressure ramps at the SNUADC's drift against the PC, measured without its stamps or resets. In recordings with whole reset intervals it agrees with them (−63 ppm; median difference +1.5 ppm, 581 recordings). It is too noisy per recording, and in recordings under about 4 h its rate is biased toward zero, so it cannot yet speak for recordings without resets.
Clock corrections in every file	2026-10-11	current	A scan of all 6,388 files for the jumps where the recorder re-synchronises a device's stamps. Each device type has its own correction signature; only SNUADC and BIS correct clearly enough to measure their drift.
Physical units, shared drift and time order	2026-10-11	current	Device drift rates cluster into units: about 8 SNUADC boards and 8–18 BIS monitors. Part of the drift is shared by both devices of a case and changes between cases: the recorder PC's own rate. Case order carries no time information.