Patrick Dempsey · October 22, 2026 · 5 min read
You check in the morning. There's a number on the watch. There's another number, also called HRV, a little further down the same app. If you wear a chest strap or use a second platform, there's a third. None of them agree, and the gaps aren't small.
The natural conclusion is that one of them is broken. None of them is broken. They're different calculations, and they were never meant to be compared.
Below: what the two main statistics actually measure, why the disagreement is designed in rather than a fault, and the rule that makes any of this usable.