What each one actually measures
The pad measures the belt. It drives the motor, so it knows belt speed and belt distance directly — how far the surface under your feet actually travelled. For distance, that is ground truth. Steps on the pad's display are less settled: some pads count them with a sensor, others derive them from speed, and some report only distance with no step figure at all. Calories on a pad display are usually a table lookup — speed times minutes — that knows nothing about you.
The Watch measures your wrist. Steps and indoor distance come from a stride model fed by arm motion. Heart rate it measures genuinely well, and its calorie estimate uses that plus your personal metrics. But at a desk, the stride model's input is garbage: a wrist resting on a keyboard can read as almost nothing, and stray arm movement can read as more walking than the belt did.
The verdict, metric by metric
| Metric | Trust | Why |
|---|---|---|
| Distance | The belt | Measured directly from the motor. The Watch infers it from a wrist that isn't participating. |
| Steps, at a desk | Belt-derived | Distance divided by your stride beats a motionless wrist. Honest apps label these as estimates, because they are. |
| Steps, free walking | The Watch | With arms swinging, the Watch is very good. This is the walk it was designed for. |
| Heart rate | The Watch | On the wrist, where the sensor was designed to sit. Ankle readings are folklore. |
| Calories | Nobody, fully | The pad's number is a crude table. The Watch's is a better-informed estimate. Nothing at home measures energy; everything estimates it. |
Why calibration doesn't reconcile them
Apple's advice — walk outdoors with GPS to calibrate — genuinely improves the stride model. For walks where your arms swing. Desk walking doesn't mistune the model, it removes the model's input, and no amount of calibration restores data the wrist never produced. Owners recalibrate, see the same gap, and conclude something is broken. Nothing is. The tool doesn't fit the job.
The calibration that does matter is on the belt side: stride length, if steps are derived from distance. Count a hundred steps on the pad, read the distance covered, divide. That number turns true distance into honest steps.
Use each instrument for what it measures
The setup that stops the arguing: let the belt supply distance and steps, let the Watch supply heart rate, and let a workout record tie the walk together in Apple Health. No single device at your desk does all three well. Two of them together do.
How Waalk records it
Belt numbers, labelled honestly.
Waalk records the belt's own distance, to the metre, every second over Bluetooth. Steps are derived from that distance and your stride — 63 cm by default, calibrated in a minute — and labelled as estimates in Health. Energy is written as a net estimate, never copied from the pad's calorie table. The walk lands as an Indoor Walk workout, and your Watch stays on your wrist doing what it does best.
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