HKQuantityTypeIdentifierStepCount — why your Apple Health step total is too high
HKQuantityTypeIdentifierStepCount is the most-exported identifier Apple has, and the most commonly summed wrong, because two devices on the same body both write it.
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Two sources, one walk
Your iPhone counts steps from your pocket. Your Watch counts them from your wrist. During any walk with both, the export holds two overlapping series for the same minutes, each a full HKQuantityTypeIdentifierStepCount record with its own sourceName. Sum every record and you roughly double the walk. The Health app shows a sensible total because it de-duplicates by source and priority; a raw export does not.
De-duplication is a policy, not a sum
Resolving overlapping step sources is exactly the problem our §6.4 stage exists for: when two devices claim the same interval, one wins by a priority rule, and the loser’s overlap is dropped rather than added. This page counts your steps the way the Health app does — by source, not by blind addition — so the number matches what your phone shows.
This identifier is one of dozens. The Apple Health data dictionary lists every identifier this parser reads, with its canonical type and unit.