Why do they have to put jewels inside of watches?
Analog watches have a lot of gear wheels mounted on tiny axles. For the watch to work for years, these axles have to have very low friction bearings that don’t wear. Several hundred years ago, it was realized that gem stone, such as sapphire and ruby, could be shaped with an indentation is one side (hole) that would take the end of the axle and provide just such a bearing and last for decades. So watches have jewels and the more of their axles have jeweled bearings, the more accurate the watch is likely to be and thus “better”.