And your own can vary when doing the exact same exercise too - like say treadmill at 3.5 mph.
A tired stressed day it could read high.
A nice recovered day could read normal.
A day being dehydrated or gym AC not working great could read high.
Side point - that's why HR-based calorie burns may sometimes be the best option for getting a calorie burn, but it can have it's own caveats and issues too since it's not an exact science.
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