What Do 17 Jewels and Incabloc Mean on a Watch Dial?

Vintage dials are full of small print: 17 Jewels, 21 Rubis, Incabloc, Antimagnetic. Here is what the two most common terms mean.

Jewels

Jewels are tiny synthetic rubies used as bearings inside the movement. Metal pivots turn in them with very little friction and wear, which keeps the watch accurate for longer.

7 jewels: a basic movement.
15 to 17 jewels: a fully jewelled manual-wind movement. 17 is the classic number.
21 to 25 jewels: common on automatics, where the winding system needs extra bearings.

More jewels than this rarely means better timekeeping. Rubis is simply the French word for the same thing.

Incabloc

Incabloc is a shock protection system introduced in 1934. The balance wheel, the most delicate part of the watch, sits in jewels held by a small lyre-shaped spring. When the watch is knocked, the spring lets the jewel move and then return to position, so the fine pivot does not break.

Antimagnetic

This means parts of the movement are made of alloys that resist magnetism. It helps, but a vintage watch should still be kept away from speakers, phone cases with magnets and bag clasps.