A cylindrical-shaped synthetic gemstone (usually a ruby) with a hole in the centre. Jewels are pressed into plates, bridges and taps to reduce friction and minimise wear in pivot holes drilled into planar components. The rapidly rotating pivots of a gear train rotate inside the jewellery. In very fine watches, the walls of the holes in the jewellery are not cylindrical, but are rounded into an olive-like shape, hence the technical term 'olive' or 'olive-cut jewellery hole'. The rounding on the walls of the hole further reduces friction in the bearing because it minimises the contact area between the jewel and the pin. In addition, an olive-cut jewel hole gives the pin greater freedom of movement.

Pallets fitted with ruby jewels.

To reduce friction in precise watches, precious stones are inserted at critical points, e.g. on the impulse faces of pallets and the impulse pin (roller pin). In the past, natural precious stones (e.g. rubies or sapphires) were used. Nowadays, most modern watches are based exclusively on synthetically manufactured jewellery. One can distinguish between bearing jewellery with holes, end stones (cap jewellery), pallet jewellery and roller pins (impulse pins). Just because a movement has a large number of jewels does not necessarily mean that it is a particularly high-quality movement. On the contrary: the dial of a cheap wristwatch may boast that the movement contains a large number of 'jewels', which could lead an uninformed person to assume that it is a high-quality watch.

The familiar cycle of three ordinary years of 365 days followed by a leap year of 366 days was initiated by the Roman emperor Gaius Julius Caesar. The year was defined by the Julian calendar, however, is 0.0078 days longer than the actual astronomical year. Pope Gregory XIII corrected the error, which had accumulated to ten full days over many centuries, by instituting the Gregorian calendar in the year 1582.