I've been sleep tracking with my Garmin Fenix 7 for about 18 months, and to me it seems bang on. The HRV stat is particularly good - a decline over about a week

I've been sleep tracking with my Garmin Fenix 7 for about 18 months, and to me it seems bang on. The HRV stat is particularly good - a decline over about a week predicted the onset of flu symptoms a couple months ago, for example. Body battery is also a really useful feedback measurement. Sleep onset and wake times are right; REM seems right; and deep/shallow measurement at least correlates with how I feel.