Pre-WWII pocket watches have round balance jewels, but most post-WWII mechanical watches seem to have "figure eight" balance wheel jewels (as shown below on Juvenia). I assume the balance jewel is shaped like a figure eight because of an "incabloc" thing, but I would be grateful for an explanation.

hi Ethan; I think perceptions can be deceiving!!! The jewels are round,but end cap jewels have the hour glass which is a thin spring device and attached at one end over them, giving the jewels (and the balance staff) a bit of cushion under shock and I that's how the Incabloc works. The illustration is of two point contact and three point contact systems which I think more clearly shows that the jewels are round but held in place under tension by the incabloc or other system

Thanks for the explanation.

You are very welcome Ethan, and after all, you were most helpful to me some time back on my IWC Shaffhaussen.It is my pleasure to help,sir!!!