(First photo) Past Forerunner models made use of a simplified glue construction which made it easier to heat-soften the glue and remove the screen by prying or by suction.

(Second photo) This watch (and other recent models) makes use of a complicated glue construction which makes it more difficult to heat-soften the glue and remove the screen by prying or by suction.

For more detail, the 3D models used to produce these images are available at these links: (old, new) and can be opened in your browser at https://openjscad.azurewebsites.net/.

Watch body

Glue

Bezel

Screen