Apple Watch running the original 1.0 software rather reliably recorded a user’s heart rate every ten minutes. With Watch OS 1.0.1, users noticed that heart rate records were no longer being kept as frequently. This was initially thought to be a bug but Apple has now clarified that this is intended behaviour on its website.
The updated website says that ‘Apple Watch attempts to measure your heart rate every ten minutes, but won’t record it when you are in motion or your arm is moving’. The original version of this feature did not care about arm movement.