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.


Clock	Pulse oximeter frame clock
Measured against	SNUADC sample clock
Modes	all
Status	measured
Drift	18–52 ppm by setup
Correction size	32.3 ms (IQR 30.4 to 34.8)

Correction¶

One repeated 33.3 ms frame whenever a frame of lag has built up (a slip). physiosync detects the slips in the beat-matched ECG→PPG delay and removes the sawtooth tooth by tooth.

Parameters¶

Parameter	Value	Status	From
PPG sawtooth rate	18–52 ppm by setup	measured	The PPG sawtooth and its correction
PPG slip size	32.3 ms (IQR 30.4 to 34.8)	measured	The PPG sawtooth and its correction

Evidence¶

Study	Date	Status	Summary
The PPG sawtooth and its correction	2026-10-10	current	The ECG→PPG delay creeps at 18–52 ppm and jumps up by one 33.3 ms frame at each slip, every 11–31 minutes. A tooth-by-tooth model removes it; where the correction is confident it is essentially exact on injected test data.