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Briefly, in the days before electronic watches the watch movements were full of gears, to reduce the wear on the gear movements the watch makers would use jewels such as ruby to make the bearings for the gears. The jewels were much harder than steel and would last longer. A watch with a lot of jewel bearings would last longer and be worth more money.
This article will explain it.
http://www.horologist.com/balance_jewels...
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