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BIS clock

The BIS monitor's own clock.

Stub

Imported from the time-source table; the full page is still to be written.
Type oscillator
Nominal 128 Hz EEG sample clock
Kept by BIS monitor

Description

The BIS monitor's own clock. Its EEG stamps drift by about +25 ppm against the recorder PC and are corrected on a fixed 8,192 s timer.

Route to UTC

The route the atlas trusts most (2 links; its weakest link is measured apart from the link to UTC that every clock shares):

BIS clock
link measured BIS against the recorder PC: drift 25 ppm (p10–p90 12 to 50; 5th–95th 7.3–51.1 ppm; census fit of 4,728 recordings median 21.1 ppm); corrected every 8,192 s (2 h 16.5 min), ± 20 s in 95% of intervals
Recorder PC clock
link assumed Recorder PC against UTC: drift 0.1–10 ppm (assumed); corrected every 8–24 h (assumed)
UTC
Where every route ends.

Independent checks. 3 other routes reach UTC; where they meet, the offsets must close around the loop:

Plan. Two routes, and they close: through its own stamps to the PC, and through shared bursts to SNUADC. A constant latency (−0.80 s or −0.66 s by SNUADC mode, whole release) belongs in the link. To strengthen: use the cardiac artefact where there are no bursts.

Link Clock Against Modes Rate Corrected every Status
BIS against the recorder PC BIS clock Recorder PC clock all 25 ppm (p10–p90 12 to 50; 5th–95th 7.3–51.1 ppm; census fit of 4,728 recordings median 21.1 ppm) 8,192 s (2 h 16.5 min), ± 20 s in 95% of intervals measured
BIS against SNUADC BIS clock SNUADC sample clock all −72 ppm (IQR −82 to −54) — measured

Variables stamped by this clock

BIS index

Variables spaced by this clock

BIS EEG

Observations

Observation Status Summary
Device clock drift depends on the setup established The drift of the SNUADC's and the BIS's timestamps against the recorder PC is largely set by the setup: knowing a recording's PC key (the serial ports of its four core devices) puts the SNUADC's drift within 3 ppm of its setup's median in 97% of cases and the BIS's in 83%, against 34% and 17% for the release's median. On the whole release's correction intervals the same test gives 71% and 60% (Identifying the recording setup of every case).
The EEG–ECG offset is fixed by the SNUADC correction mode established After the stamp model, BIS EEG still lags the SNUADC ECG by a constant: −804 ms in step mode and −660 ms in frequent-correction mode over the whole release, tight within a port or unit. The mode, a property of the setup, sets the constant.

Studies

Study Date Status Summary
Gaps and unbroken segments in every waveform 2026-10-19 draft Every gap and every unbroken segment in the 6,388 recordings, per waveform. The curves are not smooth: a cliff at about 18 s in every device marks the recorder's pauses, SNUADC segments stop at 5 hours, Primus segments at about 2.0 hours and BIS segments at about 2.3 hours (each device's correction cycle), and BIS's short gaps grow with the time since the last one (clock resynchronisations, not lost data).
When each device's clock is corrected, in every recording 2026-10-19 draft From the steps between records in all 6,388 recordings: the BIS is corrected every 8,192 s and the Primus every 7,230 s, on their own timers (the first correction comes at any time after the device starts); the SNUADC is reset when 0.49 s of drift has built up. With the full rerun of the correction fit, it gives each device's drift against the recorder PC in 4,728 BIS and 2,728 SNUADC recordings, and shows that the Primus's 20–23 s AWP pauses belong to its correction cycle. Every rate here is relative to the recorder PC, whose own clock drifts and is corrected.
Message sizes and the steps between records 2026-10-19 draft Every record in every waveform: SNUADC writes messages of 100 samples (0.2 s), Primus 30 (0.48 s), BIS 16 (0.125 s), CardioQ no fixed size. Backward steps outnumber gaps by about a hundred to one and come from a few recordings with duplicated or interleaved records. Primus gaps are whole lost messages; most SNUADC and BIS gaps are not.
What each break in the stamps is 2026-10-19 draft Every step between waveform records in the release, sorted by mechanism: written twice, a SNUADC clock reset, interleaved streams, a pause shared by every device, whole messages, less than a message, or a fraction of a message beyond whole ones. A continuity test with controls shows which classes lose data: shared pauses and most longer SNUADC gaps do; steps under one message, and SNUADC's lone one-message steps, mostly do not.
How often each device is corrected 2026-10-17 current The devices re-synchronise in different ways: SNUADC when its drift reaches about half a second, BIS on a fixed 8,192 s timer, and the Primus by small steps about every two hours that do not keep up with its drift (+104 ppm, measured later by breath matching).
Recorder PC clock steps and recording pauses 2026-10-17 current A step of the recorder PC clock would move every device's stamps at once. Searching all 6,388 files for such simultaneous jumps found none of 0.5 s or more; what moves everything together is recording pauses.
Closing loops in the timing graph 2026-10-13 current Where two independent routes reach the same clock, the offsets around the loop must sum to zero. Three measured loops close within their noise; the BIS loop closes up to a constant latency; the proposed EMR loop is not a loop at all.
The cardiac artefact in the BIS EEG 2026-10-12 current The BIS EEG carries a weak electrical trace of every heartbeat. Too weak for beat-by-beat matching, it shows clearly when averaged on the ECG's R peaks, and gives a second SNUADC–BIS timing reference that agrees with the bursts to about 16 ms.
Shared bursts between the ECG and the EEG 2026-10-12 current Electrocautery and muscle bursts appear in both the SNUADC ECG and the BIS EEG. Cross-correlating their envelopes gives the offset between the two devices' stamps every 10 minutes: about −0.8 s, in a sawtooth that follows both clocks' corrections.
The stamp sawtooth model for SNUADC and BIS 2026-10-12 current Fitting each track's record stamps against its sample count as a drift with corrections (a sawtooth) puts SNUADC and BIS on one timeline without any artefact. Checked against shared bursts, the EEG–ECG timing error falls from about 790 ms on the recorded stamps to 33 ms with one constant per SNUADC mode in the pilot, and 42 ms over the whole release.
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.

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