Why are there Jewels on movement?

It is interesting question. when I first time saw the twenty-one jewels on the backside of Mechanical Automatic Watch movement. I wondered why jewels on there. after got involved more about the movement and talked to the guy who worked in movement factory. finally got the answer for it.

Secondly, these jewels are in the gears of movement to reduce the friction. for example, like the lubricating oil for your bicycle, but you know movement is inside of watch, so Jewels helps it. for Mechanical movement, normally with 17 jewels up, mostly them in 21-29 jewels. the more, the better. functional, these jewels make your watch run smoothly and longer.

Thirdly, these Jewels let the watch be more accurate. the reason is Friction stops the gears in their track, more friction, then slower for the gears, slow gear means the time would be behind the actual time. Jewels in the movement are to prevent that happened. this is why more jewels, better quality for movement, more expensive for movement, and less friction. some Swiss movements would be 35 jewels up.

Fourthly, we all know the Quartz Watches movement with battery for power. no need gears. so no need jewels. but as i know, If you look at the expensive Swiss quartz movement like 704 gold, there are 5 jewels too. for expensive quartz movements, manufacturers make sure you have better experience, make few gears with Jewels. for cheaper quartz movement normally made from plastic, friction is not a problem. The same as Mechanical movement, quartz movement with jewels last longer.