Bracelet stretch

[blevine]

Just curious about bracelet stretch. (From the pictures commonly showing the level of stretch I am curious why it’s not called sag.)

More importantly:

1. What typically causes it?
2. What is physically happening to the bracelet to create the stretch?
Are the links themselves stretching or bending or are the spaces between links getting wider or something else.

I can see the jubilee being more prone to stretch since it is made from such tiny pieces. But the oyster seems like it’s links are bigger and more resistant to stretch yet I have seen examples of them stretching too.

Also when someone tightens up a stretched bracelet how do they do it?

Thank you in advance.