The case consists of following details:
Bezel is a ring on top of the timepiece that holds the glass or the crystal in correct position. They often display various numerical indicators and can be rotated in one or two directions in order to make additional records (compass, elapsed time, etc.) Due to its main purpose, this part is usually made of metal, but exotic materials such as sapphire are also a common sight in the world of luxury watches bezels.
A bi-directional rotating bezel with a navigational slide rule can serve for serious mathematical calculations and conversions, such as in-flight measuring ground speed, distance, fuel burn and wind set. But sometimes free rotation option are restricted by safety considerations. The perfect example is classical dive watch, where unidirectional bezel indications are used to measure remaining dive time. It can only be adjusted clockwise, so even if something goes wrong during you journey through the depths, your watches will tell you to get out of the water too early, rather than too late.Glass
The glass covers the dial to protect it from exterior impact.
The glass quality is determined by its shock-, scratch-resistance and transparency. The hardness of glass is checked by Vickers hardness test by applying a diamond. The hardness level is expressed in a special scale.
There are three most common glass types:
Plexiglass - a transparent plastic, soft material (up to 500 HV), which is hard to break, but easily to scratch. Furthermore, plexiglass loses its clarity with time, that is why it is used for cheap watches.
Mineral Glass has a CRYSTAL GLASS mark and its characteristics are similar to a window glass. It keeps clarity well and has a good shock-resistance. Its hardness level is about 600-800 HV, which means that a harder material like metal or stone can scratch it.
The most scratch-resistant glass is considered to be a sapphire glass with SAPPHIRE CRYSTAL mark. Its hardness reaches 2200 HV. it can be damaged only by a diamond, but in comparison to mineral glass it is easier to break. Due to the complexity of sapphire processing this type of glass has a high price.
Apart from traditional glass types there are also glass hybrids such as:
Sapflex - mineral glass with sapphire coating
Hardlex - an enhanced mineral glass
The glass is also distinguished by cut type:
Some models, as well as skeletons, have a sapphire glass instead of a case back, to make the movement visible.