Sand-blasting: Creating a granular metal finish by using a high-pressure jet of sand.

Sapphire: In the case of watches, a synthetic corundum crystal with a hardness second only to diamond (9 on the Mohs scale), not to be confused with the gem by the same name, though it does share the same scientific properties. Transparent sapphire is used for some scratch-resistant watch crystals.

Sapplex Crystal: Combination of sapphire and hardlex crystals.

Screw down locking crown: A crown which aids water resistance by sealing the crown against the case. The seal is achieved by the matching of a threaded pipe on the case with the crown's internal threads and gasketing while twisting the crown to lock it into place.

Seal: Synthetic gaskets that seal the joints between parts of the case to increase water resistance.

Second: Basic unit of time (abbr. s or sec), corresponding to one 86,000th part of the mean solar day, i.e. the duration of rotation, about its own axis, of an ideal Earth describing a circle round the Sun in one year, at a constant speed and in the plane of the Equator. After the Second World War, atomic clocks became so accurate that they could demonstrate the infinitesimal irregularities (a few hundredths of a second per year) of the Earth's rotation about its own axis. It was then decided to redefine the reference standard; this was done by the 13th General Conference on Weights and Measures in 1967, in the following terms: "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the fundamental state of the atom of cesium 133". Conventionally, the second is subdivided into tenths, hundredths, thousandths (milliseconds), millionths (microseconds), thousand-millionths (nanoseconds) and billionths (picoseconds).

Setting (to time): Process of bringing the hands of a watch or clock to the position corresponding to the exact time.

Shock-absorbers: Spring devices in balance-wheel bearings that divert shocks away from the fragile pivot (usually 12/100mm diameter) to the sturdier parts of the balance staff. The springs allow the balance-wheel to return to its original position after shocks.

Shock resistance: The level to which a watch can withstand normal wear and tear, culminating in handling strenuous sport activities. The higher the rating, the greater the durability.

Shot-blasting: A satin finish obtained by using tiny glass pellets, one or two microns in diameter.

Skeleton movement: A watch movement, usually mechanical in nature, in which the parts have been constructed in more of a sparse design resulting in more of a skeletal see-through appearance. They are usually more expensive than a non-skeletonized counterpart, and are often beautifully finished and decorated.

Skeleton watch: Watch in which the case design enables the main parts of the movement to be seen.

Slide rule bezel: A rotating bezel that is printed with a logarithmic scale and assorted other scales and is used in conjunction with fixed rules of mathematics to perform general mathematical calculations or navigational computations.

Solar-powered: A type of quartz movement where the batteries are recharged via solar panels on the watch face. They have a power reserve so they can run even in the dark.

Solid State: A timepiece with no moving parts. All digital watches are 100% solid state. Analog watches combine solid state circuits with moving parts.

Split-seconds: A second chronograph that runs concurrently with the first but can be stopped independently to record an intermediate time. It the catches up to run with the first hand again.

Split time measurement: Measures the elapsed time of a certain moment of an event, while overall continuing to time the entirety of the event.

Stainless steel: An extremely durable metal alloy (chromium is a main ingredient) that is virtually immune to rust, discoloration, and corrosion; it can be highly polished, thus resembling a precious metal. Because of its strength, stainless steel is often used even on case backs on watches made of other metals. The most common in watches is 316L steel, which indicated surgical grade, or hypoallergenic properties. Some watches (Rolex and XOskeleton to date) may also use the more expensive 904L steel.

Sterling Silver: A white and highly reflective precious metal. Sterling refers to silver that is 92.5 percent pure, which should be stamped on the metal, sometimes accompanied by the initials of the designer or country of origin as a hallmark. Although less durable than stainless steel and other precious metals, sterling silver is often employed in watches that coordinate or look like sterling jewelry. A protective coating may be added to prevent tarnish.

Stopwatch: Timekeeping instrument which can be used for measuring intervals of time. When this is incorporated into a wristwatch, the resulting complication is known as "chronograph".

Strap: A watch band made of a flexible material such as leather, plastic, rubber, or fabric.

Subdial: A small dial within the main dial of a watch and used for any of several purposes, such as keeping track of elapsed minutes or hours on a chronograph or indicating the date.

Sun/moon indicator: A wheel on a watch partially visible through a cut-out window indicating a sun and moon on a 24-hour basis. Also known as a "day-night indicator".

Super accurate: A quartz movement that utilizes patented integrated circuit technology, assuring their accuracy up to 20 times more accurate than conventional quartz movements.

Sweep seconds-hand: A hand that moves in a fluid sweeping motion, as opposed to the pulsing motion found on most quartz watches, and dedicated to illustrating the passing seconds. This sought after feature is most commonly found in conjunction with mechanical movements, though some quartz movements may exhibit it as well.

T

Tachymeter (also tachometer): A watch function that measures the speed at which the wearer traveled by means of a numeric scale on the watch bezel of a chronograph. Frequently used to determine a speed of a car over a measured distance.

Tank watch: A rectangular watch with heavier bars on either side of the dial, inspired by the tank tracks of World War I and first created by Louis Cartier.

Telemeter: A watch function that finds the distance of an object from the wearer by measuring how long it takes sound to travel that distance. Like a tachymeter, a telemeter consists of a stopwatch function and a special scale on the dial of a chronograph.

Timer: Instrument used for registering intervals of time (durations, brief times), without any indication of the time of day.

Titanium: The "space age" metal, often with a silvery-gray appearance. Because it is 30 percent stronger and nearly 50 percent lighter than steel it has been increasingly used in watch making, especially sport watch styles. Its resistance to salt water corrosion makes it particularly useful in diver's watches. Since it can be scratched fairly easily, some manufacturers use a patented-coating to resist scratching.

Tonneau watch: A watch with a barrel-shaped case with two convex sides. The term is derived from the French word for "wine caste".

Tourbillon: A complex piece of micro-engineering which results in the escapement of a watch rotating on its own axis. the object of the exercise is to cancel out the variations in running regularity which can be caused by the watch being in different positions, predicated on the theory that a watch may gain in one position yet lose in another. It is more prized for the achievement of its creation by hand as opposed to its proven effectiveness, and is a highly coveted and expensive complication.

Tritium: An isotope of hydrogen used in the luminous compounds which give watch dials and hands their glow in the dark capabilities. Many watch dials will show a small T at the bottom, indicating the use of tritium. The half life of tritium is 12.5 years thus it will lose its ability to provide illumination as time passes. Now largely superseded by non-radioactive organic compounds such as the trade name Luminova.

U

Unbalance: Disequilibrium of a rotating part.

UTC: Universal Time Co-ordinated. A universal time based on the Greenwich Meridian used by the military and in aviation. Greenwich Mean Time (GMT) can be considered approximately equivalent to UTC. GMT seems to be a more common reference among watch enthusiasts, though some argue that that the term is being replaced by UTC. Using this timezone/standard avoids errors and problems associated with different timezones and summer times operational in different countries.