Christian Zibreg, iDownloadBlog:

Complications—small elements rendered on the Apple Watch face that provide quick access to frequently-used data—have received a boost on Series 4: all-new templates now let brand new elements, such as full-color images, text and gauges, follow curvature of the display.

Complications are a great way to connect users to their favorite apps with every wrist raise and keep them informed throughout their day. Tapping a complication launches its underlying app.

Terrific post, lots of interesting detail.