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Watch Glossary and Term - J

Jewels: In the mechanical watch and some quartz watches, jewels (usually made from synthetic ruby) are used as bearings for those parts of the movement subject to constant motion. They are not valuable at all in the monetary sense but they are valuable in aiding the precise running of a watch over a long period and reducing wear. It is a fallacy that the more jewels the better the watch. A basic handwound mechanical usually comprises 17 jewels which in the main is the optimum count. Automatics may require more for the winding mechanism itself. In the 1960s there appeared to be a competition to see who could fit the most jewels in a watch movement, manufacturers proudly referred to 100 Jewels on the dial; opening the watch usually revealed that up to 80% of these jewels had no purpose and were simply mounted here and there on the movement to up the jewel count!

Jumping Hour: System of timekeeping whereby the seconds and minutes are shown by traditional hands but the hour is shown in a dial cutout (often at 12), on the minutes hand reaching 59 minutes, the hour disc under the dial will jump to the next hour.