CGM Sensor Drift & Interstitial Lag Simulator

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Sensor wear

Wear-time day Day 1

How many days this CGM sensor has been under the skin. Uncorrected drift keeps growing the longer it stays in.

Drift rate 1.6 mg/dL/day

Interstitial lag 9 min

Fingerstick calibration

Calibration interval

True blood glucose

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Time of day

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Uncalibrated CGM

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Error (uncal)

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Periodic-cal CGM

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Error (cal)

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How it works

A CGM's tiny filament sits in the interstitial fluid under the skin, not in a blood vessel, so its raw signal trails true blood glucose by several minutes — most visible right after a meal spike or a fast drop. On top of that lag, the electrochemical sensor slowly drifts as biofouling and local tissue reaction change its response over its multi-day wear life, adding a growing offset if nothing corrects it.

interstitial(t) = lowpass(trueBG(t), τ_lag)
drift(t)        = rate · hours_since_last_calibration
CGM(t)          = interstitial(t) + drift(t) + noise

Wear-time day — how far into the sensor's life the uncalibrated trace has drifted.
Drift rate — how fast the electrochemical baseline wanders per day of wear.
Interstitial lag — the time constant of the fluid-diffusion delay; both traces share it.
Calibration interval — how often a fingerstick reference resets the periodic trace's drift to zero; the blood-drop icon on the arm marks each event and the sensor patch flashes green as its baseline snaps back into alignment on the chart.

Real-world relevance: this is exactly why real CGMs (Dexcom, Libre, Medtronic) either ask for periodic fingerstick calibrations or ship factory-calibrated with tighter drift tolerances — without a periodic true-blood-glucose anchor, sensor drift alone can push a reading dangerously far from reality by the end of a 10–14 day wear cycle.

True blood glucose Uncalibrated CGM Periodic-cal CGM Calibration event

🩸 CALIBRATED — baseline reset

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