SNUADC stamps run −0.95 ppm against the sample count¶
Between corrections each 0.2 s record stamp increment is about 0.19 µs short: stamps run −0.95 ppm from the sample count in 88% of files (both SNUADC modes). It is arithmetic, not clock drift. The other 12% sit between −0.90 and −0.55 ppm.
| Status | established: shown on many cases, with a control. |
| Devices | SNUADC, Vital Recorder |
What it means¶
Rates read from stamps include −0.95 ppm; the frequent-correction mode's "about −1 ppm" is this, not drift. Placing samples by rounded stamps, as the vitaldb package does, overwrites one sample about every 35 minutes.
What is done about it¶
The TimeNet import places samples by count, so no sample is lost. The census of all files (17 October) confirmed it.
Evidence¶
| Study | Date | Status | Summary |
|---|---|---|---|
| SNUADC stamp arithmetic | 2026-10-17 | current | Between corrections the SNUADC block stamps run −0.95 ppm against the sample count: each 0.2 s increment is about 0.19 µs short. This, not clock drift, is the "about −1 ppm" seen in frequent-correction mode. |
| Paced ECG as an independent clock | 2026-10-17 | current | Fixed-rate pacing gives a clock the recording chain cannot touch. Timing paced beats on three timelines shows that each SNUADC step-mode correction loses about 18 ms of signal, and that nothing else breaks the sample stream. |
| The vitaldb package's loading conventions | 2026-10-17 | current | The vitaldb Python package sets time zero from the tracks loaded, places waveform blocks by rounding their stamps up to a sample, and lets overlapping blocks overwrite each other. Each choice moves or loses samples. |