This is a longish and more advanced article coming from one of my ebooks, precisely "The Patreon Chronicles" (available in the Classroom here for purchase). It details jewels in watches, and complements the article about mainplates published earlier. _______________________________ What are the functions of a ruby or other precious-sounding gems in watch movements? While watches are considered among the rare items composing men’s jewelry, we need to understand the main differences between jewels “in” a watch and jewels “on” a watch. The words “ruby” and “precious stones” are indeed most evocative, but the reality is much more prosaic if we examine the application of these precious stones into watchmaking micromechanics. So, we’re not considering the precious stones that people display over their watches, and instead, check the much less glamorous aspect of what stays inside the watch: its heart, that is, the movement. First of all, let’s start by examining a real-life case. What you see below is a cheap watch movement called EB 8800. It was produced in mass quantities in the Seventies, and it is a relatively simple affair - equivalent to the cheap quartz-based calibers of today. As you can see, the top bridge has writing etched on it which says “Swiss - Unadjusted - One Jewel.” And the only jewel here is quite visible: it is the ruby located on the top of the balance wheel, at three o’clock. Apart from this, you can see the circular depressions in a lozenge-shaped array in the center of the watch. There are tiny holes practiced into them, and they host the pinions of the wheels turning inside the movement. You can see one of the wheels quite clearly next to the “EB” logo, with its teeth. Now, let’s check another photo of another movement. The movement is similar, but looking closely, you can spot a few key differences. Precisely, the very holes we talked about before showing the application of rubies, similar to the one over the balance wheel. Why the first movement has none, and the other does?