A Mechanical wrist-watch with the addition of a "Rotor". The rotor is attached the back of the movement & when the watch is in motion (regular wear) the rotor spins around the inside of the watch & "automatically" winds the watch, thus eliminating the need to constantly manually wind the watch. It is important to understand that an automatic watches also require a manual wind every so often. An automatic watch that is at the end of its power reserve due to non-wear, or an automatic watch that has completely stopped due to non-wear must be manually wound 30-40 times. This ensures that when you put the watch on after a manual-wind you begin the cycle at a full reserve. Thus as long as you wear the watch it will remain fully wound & if removed the watch will stay working for the specified amount of time as indicated in your manual (generally 35-45 hours).

The Buckle is the mechanism that fastens the strap or bracelet around your wrist.

• Tang Buckle: Is a traditional Loop & Pin (belt type) buckle.
• Deployant Buckle: Is a buckle that attaches to either side of the strap. The buckle is expandable so that the watch can be slipped on the wrist & snaps shut on the wrist. Once set to the correct size it needs not be resized, thus reducing stress to the stress & elongates the life of the strap. This buckle also offers additional security while putting on & taking off the watch.
  

A "Bezel" is a ring on the top side of the case around the crystal with time intervals engraved. The "Bezel" can be turned "Bi-directional" - both clock-wise & counter clock-wise, or more popularly "Unidirectional" or counter clock-wise. The purpose of the "Bezel" is to be able to begin timing an event at any given time by aligning the bezel's #12 at the beginning point.

• Uni-Directional Turning Bezel: A bezel that turns in only one direction (counter-clock wise). The purpose is to measure the length of dive-time you are under water, should the bezel accidentally move, it will only indicate shorter remaining dive time. Thus eliminating the risk of being left without oxygen.

Case:

The "Case" is the total housing of the watch excluding the strap or bracelet. The case is the housing of the Dial (face), movement & crystal (glass).

A watch that bears a COSC certification is called a "Chronometer". A Chronometer watch has passed a vigorous 7 day test in extreme hot & cold, in various different positions.

• Mechanical watch: A mechanical watch (manual-wind or automatic wind) that maintains -4 to +6 seconds per day accurate during this test earns a COSC certification.
• Quartz Watch: A quartz watch (battery operated) that maintains an amazing +/-0.2 second per day accuracy during this test earns a COSC certification.

The "Crown" is the knob that adjust the time & date of the watch. For an automatic or manual wind watch the crown doubles as the winding mechanism to power the watch.

The "Crystal" is the glass that you look through in order to see the "Dial" (face). The purpose of the crystal is to protect the dial. The Crystal can be made of glass, plastic, or a highly scratch resistant synthetic material called "Sapphire Crystal".

The "Dial" is the face of the watch showing the time. A blue dial means the face color of the watch is blue.

The "Display" is the term used to describe the way a watch displays the time. A "Digital Display" will show the time by showing a digital image of the numbers in a window. An "Analog Display" will show the time by two hands sweeping the dial.

The EOL indicates when it is time to replace the existing battery. Different manufacturers use different methods to indicate a low battery, i.e. a second hand will tick once every few seconds instead of every second... 

There are various different ways that the metal of the watch can finished. The three most common finish

• Polished surface - has a shiny high gloss finish which is reflectant.
• Brushed Finish - surface has a galvanized, satin or matte finish which is non-reflectant. 
• Gold Plated Finish is a thin layer (usually around 5 microns) of gold electroplated to Stainless Steel base.

"Function" is a term used to describe the different tasks each time related component performs. i.e. the date "Function" is the date task the watch performs.

Watches with steel or gold bracelets made of individual attached components. Each individual component is called a "link".

"Luminous Hands and/or Hour Markers" - is a standard feature on many watches. The hour markers and/or hands have a coating of "Glow in the dark" which will illuminates in the dark so you can tell the time where there is insufficient light. Results vary by the amount & quality of Luminous material used.

Manual Wind Movement:

A Mechanical Movement that requires manual-winding of the crown to wind the mainspring which gets the watch going.

A "Mechanical Movement" is the term for watch that runs without an outside electrical source. The watch's mechanism is composed of multipl parts, gers, screws & springs. By winding the mainspring (either manual-winding or via automatic winding) the watch will begin to operate.

Moonphase:

A watch with the phases of the moon indicated in a sub-dial. The sub-dial will show the moon as it wanes & waxes.

The "Movement" is the motor of every watch. The Movement controls all aspects of the watch such as the time, date, chronograph functions etc.

A watch that corrects various calendar dates.

• Annual Calendar: A mechanism that automatically corrects long and short months, These watches generally do not account for leap years & requires the 1 correction on February 29th every 4th year.
• Perpetual Calendar: In additional this watch will calculate & correct for the February 29th date on leap years.

This complication displays an indicating feature which allows seeing the amount of power a mechanical watch has. This is a helpful complication that actually may help indicate problems with the watch otherwise unseen. I.E. a watch that stops while the Power Reserve shows that the power is still full - with a regular watch you would need to run time consuming tests while with a PR indicator you can immediately identify the problem.

A battery operated movement. The Quartz Movement is a watch with a mechanism powered by a "Quartz Crystal". The crystal vibrates when placed in an electronic field, thus powering the watch. Most affordable watches today have Quartz movements.

The "Sapphire Crystal" is a type of glass that covers the watch dial (face). Sapphire crystal is a made of a synthetic material, which is extremely durable, shatter proof & scratch resistant. Therefore Sapphire crystal is popularly used by all manufactures for most of their watches.

Where the crown is threaded & tightens to the case by screwing the crown into a matching threaded tube that is part of the case. The crown has a gasket that is compressed & seals the opening when the crown is tightened - thus ensuring water resistance. A Screw-Down Crown is an essential feature for any watch you intend on swimming with. An additional benefit of the Screw-Down Crown is that the crown is somewhat more protected from accidental knocks.

Tourbillon:

Common feature in chronograph watches. Measures the speed over a predefined distance. The wearer starts the chronograph when passing the starting point and stops it when passing the finish. The wearer can read the speed in units per hour off the tachometer scale. The scale is generally engraved on the bezel or printed on the outer diameter of the dial.