Apple Watch has 100 million active users.
Apple is betting that 90 million of them will open the Health app tonight, glance at a number, and trust it completely without ever asking where that number actually came from.
A former Apple Health engineer sat down with me and said something that changed the way I look at my own wrist every single morning:
"Almost nothing your watch shows you is a direct measurement. It's a model. And most people have no idea they're reading a guess dressed up as a fact."
He spent years inside the team that decides how confident that number on your screen should look regardless of how confident it actually is.
Here's what he told me, and exactly what to fix tonight. 🧵