I’ll note as well that these are next to impossible to find without flaws, and I see none on this one. Special procedures must be observed to see these installed without introducing flaws. That said, they are quite likely very dirty and need serious cleaning.
VTF Vintage Glass Pocket Watch Crystal 20-2/16 (~45.4mm) – NOS
Typical Mi-Concave Pocket Watch profile. That said, they are quite likely dirty and need serious cleaning. Images do an adequate job of representing the item. Fulton Watch Crystal Corp Fit-Tite Catalogue No. 2 – reprint.