Shock resistant is a common mark stamped on the back of wrist watches to indicate how well a watch copes with mechanical shocks. In a mechanical watch, it indicates that the delicate pivots that hold the balance wheel are mounted in a spring suspension system intended to protect them from damage if the watch is dropped. One of the earliest and most widely used was the Incabloc system, invented in 1934. Before the widespread adoption of shock-resistant balance pivots in the 1950s, broken balance wheel staffs were a common cause of watch repairs.
Virtually all mechanical watches produced today are shock resistant. Even divers' watches (according to ISO 6425) must correspond not only with such criteria as water resistance, luminosity, magnetic resistance and strap solidity, but also shock resistance.
The International Organization for Standardization issued a standard for shock-resistant watches, which many countries have adopted. ISO 1413 Horology—Shock-resistant watches specifies the minimum requirements and describes the corresponding method of test. It is intended to allow homologation tests rather than the individual control of all watches of a production batch. It is based on the simulation of the shock received by a watch on falling accidentally from a height of 1 m on to a horizontal hardwood surface.
In practice shock resistance is generally tested by applying two shocks (one on the 9 o'clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3 kg hammer with an impact velocity of 4.43 m/s (This will deliver approximately 30 Joules of energy to the watch). The watch must keep its accuracy to +/- 60 seconds/day as measured before the test.
Anti-magnetic (non-magnetic) watches are those that are able to run with minimal deviation when exposed to a certain level of magnetic field. The International Organization for Standardization issued a standard for magnetic-resistant watches, which many countries have adopted.Incabloc shock protection system
The Incabloc shock protection system is the trade name for a spring-loaded mounting system for the jewel bearings that support the balance wheel in a mechanical watch, to protect the wheel's delicate pivots from damage in the event of physical shock, such as if the watch is dropped. It was invented in 1934 by Swiss engineers Georges Braunschweig and Fritz Marti, at Universal Escapements, Ltd, of La Chaux-de-Fonds, Switzerland. It is manufactured by Incabloc, S.A. Similar systems are ETA's Etachoc, Kif, Seiko's Diashock, and Citizen's Parashock.
The pivots and jewel bearings that support a watch balance wheel are fragile in comparison to the mass they must support, and without shock protection are the part of the watch most likely to be damaged under impact. Before the widespread use of shock protection devices like Incabloc, broken balance staffs were a common type of damage requiring watch repair.
The Incabloc system uses a "lyre-shaped" spring to allow the delicate bearings to shift in their settings under impact, until a stronger shoulder of the staff contacts the strong metal endpiece, so that the pivots and bearings don't have to bear the force of the impact. When the impact is over, the springs guide the parts back to their original positions. The staff itself does not move relative to the jewel bearing, but the whole bearing is carried in a metal bushing that is free to move in the metal endpiece, under the control of the spring. Some modern balance wheels use a simpler arrangement, where, taking advantage of the low cost of modern synthetic rubies, a large jewel moves as its own mobile bushing.Water Resistant mark
Water Resistant is a common mark stamped on the back of wrist watches to indicate how well a watch is sealed against the ingress of water. It is usually accompanied by an indication of the static test pressure that a sample of newly manufactured watches were exposed to in a leakage test. The test pressure can be indicated either directly in units of pressure such as bar, atmospheres, or (more commonly) as an equivalent water depth in metres (in the United States sometimes also in feet).
An indication of the test pressure in terms of water depth does not mean a water-resistant watch was designed for repeated long-term use in such water depths. For example, a watch marked 30 metres water resistant cannot be expected to withstand activity for longer time periods in a swimming pool, let alone continue to function at 30 metres under water. This is because the test is conducted only once using static pressure on a sample of newly manufactured watches. As only a small sample is tested there is likelihood that any individual watch is not water resistant to the certified depth or even at all.
The test for qualifying a diving watch for repeated usage in a given depth includes safety margins to take factors into account like aging of the seals, the properties of water and seawater, rapidly changing water pressure and temperature, as well as dynamic mechanical stresses encountered by a watch. Also every diving watch has to be tested for water resistance or water-tightness and resistance at a water overpressure as it is officially defined.
ISO standards by standard number