New watchOS 9 feature: Heart Rate Zones.
You can view the automatically set ones in the iOS Watch app > Workout > Heart Rate Zones.
Late 20s male, not that fit, mine are as follows:
Zone 1: <142
Zone 2: 143-153
Zone 3: 154-165
Zone 4: 166-176
Zone 5: 177+
Max HR: 189
Am I crazy or is this...