S

Sapphire – see Synthetic sapphire

Screw Back - The back of the case has a thread so that it can be screwed into the case.

Screw-down crown - a crown that screws down into the case to make the watch more water resistant and to help keep out dust.

Second time-zone indicator - an additional dial that can be set to the time in another time zone.  It allows the wearer to keep track of 2 different time zones simultaneously.

Seconds Stop - the watch is stopped by pulling out the crown. This allows the time to be set precisely to a time signal.

Self-winding – see Automatic watch

Shock absorber - resilient bearing in a watch that is intended to take up the shocks received by the balance staff and protect it's delicate pivots from damage.

Shock Resistance - a watch's ability to withstand an impact equal to being dropped onto a wooden floor from a height of 3 feet.

S.I.H.H. - Salon International de la Haute Horlogerie.  A trade show held each year in Geneva. New model watches are unveiled for the trade. The show is not open to the public.

Silver oxide battery - 1.55 volt.

Six eater (6-eater) - a watch with the seconds sub-dial at the 6 o'clock position. The sub-dial covers, or "eats" the 6 o'clock marker.
Skeleton watch - the case, dial and various parts of the movement have been cut away allowing the main parts of the watch to be seen. A crystal is mounted on both the front and back of the watch.

Small Seconds - the seconds are displayed by a hand in a small subsidiary dial and not from the centre.

Solar Day - the length of time it takes the earth to rotate in 1 day using the sun as a fixed reference point.

Solar Year - The earth completes its orbit about the sun in 365 days, 5 hours, 
                    48 minutes and  46 seconds - the length of a solar year.

Sonnerie - sounds the time automatically:

                    petite sonnerie -       every hour
                    grande sonnerie -    every quarter hour


Split seconds - (German: Doppelchrono)   (French: Rattrapante) -  2 seconds hands on a chronograph.  When a button is pushed, the 2 hands start together and move in unison.  When the button is pushed a second time one of the hands stops to allow the time to be noted and the other seconds hand continues to time the event, thus “splitting” the hands.  A third push of the button makes the seconds hand that was stopped “catch up” to the hand that is still moving and once again the 2 hands move in unison. 
                    Example: You want to time how long it takes a racing car to complete 4 laps but you also want to record the time at the end of each lap.  At the end of each lap push a button and stop one of the seconds hands to record the time.  The other seconds hand continues timing.  Another push of the button starts the hands moving in unison once again.
 

Spring Bar -  

a spring-loaded metal bar mounted between the case lugs (horns) 
used to attach a strap or bracelet.

                                   Straight Spring bar

                                     Flanged Spring bar

                                The flanged spring bar is easier to remove.

Stainless Steel - an extremely durable metal alloy composed mainly of chromium. It is virtually immune to rust. Often used on casebacks of watches made of other metals.

STANDARD TIME - The time that is kept locally in each of the time zones when daylight saving time is not in use.

Stem - the shaft that connects to the movement's winding mechanism. The crown is fitted to the opposite end.

Stepping Motor - the part of a quartz movement that moves the gear train which in turn moves the watch's hands.

Sterling silver - refers to silver that is 92.5% pure.

Stopwatch - a timekeeping device used for measuring intervals of time.

Strap - a watch band typically made of leather or rubber.

Subdial -

a small dial placed inside the main dial on a watch face. Watches can have as many as four subdials (also called auxiliary dials). They give information not provided by the main watch dial such as chronographs, alarm, dual-time-zone and a calendar .
            

SUMMER SOLSTICE - the summer solstice is the longest day of the year.  The length of time elapsed between sunrise and sunset on this day is the maximum for the year.

Sweep Seconds hand - a second hand that is mounted in the centre of the dial instead of a subdial and "sweeps" the entire face of the watch.

Swiss Made - or "Swiss", or any other expression containing the word "Swiss". A watch is considered to be Swiss if:
                     1. its movement is Swiss
                     2. its movement is cased up in Switzerland
                     3. the manufacturer carries out the final inspection in Switzerland

Swiss movement - a movement is considered to be Swiss if:
        it has been assembled in Switzerland;
        it has been inspected by the manufacturer in Switzerland; and
        the components of Swiss manufacture account for at least 50 percent of the total value, without taking into account  the cost of assembly.

Synthetic sapphire - is the most expensive glass crystal material and the most scratch resistant. A very hard, transparent material made of crystallizing aluminum oxide at very high temperatures. Chemically, synthetic sapphire is the same as the natural sapphire used in jewelry, but without the coloring. Because it is so hard, it is also brittle, and shatters more easily than mineral glass or Plexiglas. Sapphire (whether natural or synthetic) is one of the hardest substances on earth. It measures 9 on a scale of 10. Diamond is a 10.
Some crystals are made of both mineral glass and sapphire. Seiko, for example, makes some watches with crystals made of mineral glass covered with a layer of synthetic sapphire called "Sapphlex".