It is a tool for solving mathematical calculations of multiplication, division and proportions, as well as problems related to distances, times and speeds. When used in flight, it allows a whole series of calculations related to fuel consumption, range and travel time to be easily performed. In addition, with a series of pre-set points to facilitate calculations, it is also possible to perform conversions between units of measurement. In watchmaking, the ring-shaped one is used, equipped with two supports that slide relative to each other: one is fixed, and is positioned along the outermost perimeter of the dial; the second is placed on the bezel, which is free to rotate in either direction. On the two supports are two logarithmic scales: the one on the bezel grows counterclockwise, while the one on the dial grows clockwise. By correctly positioning the rotating bezel (depending on the calculation to be made) in relation to the scale on the dial, it is possible to read the result on one of the two scales, at a given index on the bezel itself or on the dial. One of the most important houses to adopt the slide rule is Breitling which, with its iconic Navitimer, has created a model intended primarily for aviators and which offers, at the same time, the power of an ordinary slide rule and the portability of a wristwatch.
