Heart Rate Drift Calculator

• The chosen start-to-end elapsed time is split exactly in half. We do not split by sample count or remove pauses before finding the midpoint. Each half’s valid time can differ.
• Within a track, the previous heart-rate reading is held for intervals up to 30 seconds. Longer gaps and TCX track breaks are excluded, not filled. Explicit FIT timer pauses are reported separately.
• Speed is distance change / interval time when both cumulative distances are valid, nondecreasing and the whole interval is unpaused. Otherwise the previous recorded speed is used, if present. Distances are meters; FIT enhanced_speed takes priority, and TCX Garmin TPX Speed is meters/second. No GPS-coordinate reconstruction, grade adjustment or cycling-power mode is used.
• Heart rate and speed are time-weighted. For efficiency, both averages use the same paired intervals. Covered distance includes only intervals with usable speed; it is not the total distance of a partially missing segment.
• One FIT/TCX file, up to 8 MiB, 24 TCX activities and 100,000 records. FIT decoding stops after 10 seconds. Clear, refresh or leaving the page clears working data; your downloaded CSV remains under your control.

Aerobic decoupling compares external output with heart rate over a steady effort. Heat, terrain, stops, sensor errors and changing effort affect the comparison. This page shows descriptive arithmetic and coverage, not whether the segment was a valid test. It does not diagnose fitness, identify your aerobic threshold, prescribe training or turn a 5% coaching convention into a personal physiological cutoff. Compare other platforms only after checking their time basis, speed model, exclusions and sign convention.