Apple Watch crown doesn’t measure my BPM

Watch doesn’t measure the pulse rate using a finger, Watch uses a sensor on the back that reads the pulse at the wrist.

If you’re trying to read a cardiac rhythm (ECG) and not the pulse rate, which Watch series are you using, and are you using a Watch purchased in a country where ECG is permitted and now attempting to read the ECG in a country where ECG is permitted?

If you have not already, update your Watch to the most current available watchOS, too.

Usually it's this;

Or unpair and re-pair your watch.

Have you setup the ECG app?.

Are you in a region that supports ECG app?.

Taking an ECG with the ECG app on Apple Watch Series 4, Series 5, or Series 6 – Apple Support