A caliber can be described as the type of movement used in a watch. It is expensive and impractical to design a unique movement for each watch model, so most manufacturers often use the same movement in different watch models, sometimes with significantly different designs. The term "caliber" is due to the fact that initially the type of movement was designated by a number (in inch lines) corresponding to its largest size; however, today unique names or alphanumeric indices that are not directly related to sizes are widely used.
Knowing the name of the caliber on which the watch you are interested in is built, you can, if desired, find more detailed information about the mechanism and determine how its characteristics meet your requirements.
How to illuminate the clock face.
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Luminescent coating. A variant used in pointer dials: the hands, and sometimes the scale, are coated with a “phosphorus” coating that glows in the dark. This method of backlighting is inexpensive and can be used even in low-cost models; in addition, it does not require batteries and is suitable even for mechanical watches. On the other hand, coverage is often not as effective as it should be. The fact is that for work it must be “charged” from the sun or another bright light source, and this “charge” is enough for an average of 5-6 hours, and already in the first couple of hours the brightness of the glow drops noticeably.
— Electronic.
Illumination based on LEDs or other miniature light sources. Usually, it does not work constantly, but turns on and off by pressing a special button; the exception is LED dials (see "Dial Type"). The main advantage of electronic backlighting is efficiency: it is guaranteed to be enough to view the image on the dial. In addition, such systems do not depend on external illumination, in contrast to the luminescent coatings described above. On the other hand, the lighting requires a battery to operate; therefore, this type of illumination is found exclusively in quartz watches (see “Mechanism type”).
— Luminescent coating / electronic. Systems that combine both types of illumination described above. This option is f
...ound mainly among models with combined dials: the hands are coated with a luminous coating, and the electronic backlight is intended mainly for displays and additional scales (and also as a backup option for the hands). The combined backlight is very convenient, however, such watches are somewhat more expensive.
— Tritium illumination. Illumination option found on premium pointer dials. Miniature flasks filled with tritium, a radioactive form of hydrogen, are responsible for the illumination in such models; from the inside, the surface of such flasks is covered with a phosphor, which glows under the influence of tritium radiation. Separately, we note that this radiation does not pose a danger to humans: it does not go beyond the bulb, and even inside its intensity is extremely low. Tritium illumination is expensive, but it is extremely convenient from a practical point of view: "flashlights" work constantly, without batteries and regardless of external lighting, and shine significantly brighter than a conventional luminescent coating. However due to the decay of tritium, they gradually lose their brightness, but this happens very slowly: it takes 12 years to reduce by half, and at least 20 years for the backlight to become useless.
