Clock links¶

How one clock relates to another: drift and correction. Every rate is relative to against.


BIS against SNUADC	Measured directly from bursts seen in both the ECG and the EEG, independent of the recorder: −72 ppm (median of 191 benchmark cases), and a constant offset of about −0.8 s left after both stamp models. Per case the slope matches the difference of the two drifts against the PC (Shared bursts between the ECG and the EEG); the release medians of those drifts (+25 and −63 ppm) differ by 88 ppm, being medians over different sets of recordings.
BIS against the recorder PC	The BIS EEG stamps drift about +25 ppm against the PC (median from the correction steps of 1,939 recordings; a fit over every recording's stamps gives +21 ppm in 4,728) and are pulled forward on a fixed 8,192 s timer of the BIS's own, which does not start with the recording.
CardioQ against SNUADC	Beats matched between the CardioQ's arterial pressure and SNUADC's put the CardioQ on the SNUADC timeline within each re-anchored stretch (matched-beat MAD 0.24 s).
CardioQ against the recorder PC	The CardioQ's stamps are re-anchored about every 5 minutes, with jumps of either sign up to ±2 s.
Hospital records clock against the recorder PC	The offset between the anaesthesia record and lab systems and the recorder PC cannot be measured in the release: it is confounded with documentation lag. Entries rarely precede the device events they document.
Monitor output clock against SNUADC	The 240 Hz line in the monitor's analogue outputs runs −25 to −29 ppm against the SNUADC sample clock (6 files).
Oximeter frames against SNUADC	The oximeter's 33.3 ms frame period is fixed per setup against the SNUADC sample clock, +7 to +92 ppm across 42 PC keys, and keeps its phase through the sawtooth slips.
PPG content against the oximeter frames (the sawtooth)	The PPG content runs 18–52 ppm against the oximeter's frames, fixed per setup. When a whole frame of lag has built up, one frame is repeated: the delay steps up by 33.3 ms, then creeps down again.
Pacemaker against SNUADC	At a fixed pacing rate the pacing interval, measured on the SNUADC sample count, agrees between stretches to 0.05–0.1 ms: the SNUADC sample stream is continuous apart from the resets and gaps.
Primus against the recorder PC	The Primus stamps drift a median +104 ppm against the recorder PC (measured by breath matching through the SNUADC stamp model). Its small corrections every 7,230 s, each about 21 s after a pause in the AWP waveform, do not keep up with that drift.
Recorder PC against UTC	The recorder PC keeps Windows time, synchronised to the hospital's time server every 8–24 hours. Its offset from UTC is assumed, not observed; no step of 0.5 s or more appears anywhere in the release.
SNUADC (frequent-correction mode) against the recorder PC	In frequent-correction mode the SNUADC stamps follow the PC, with small forward steps; the −0.95 ppm they show against the sample count is stamp arithmetic.
SNUADC (step mode) against the recorder PC	In step mode the SNUADC stamps drift by tens of ppm and are pulled back by about half a second whenever the drift reaches that size, about every two hours.
Solar8000 numerics against SNUADC	The Solar8000's numbers carry no clock of their own in the release; their delay behind the SNUADC waveforms they summarise is fixed within a case, which bounds any drift of the monitor's timing.