Watch is a small clock made to be worn or carried. Most watches are worn on the wrist, but a few are carried in the pocket or worn as pendants or rings. The main purpose of a watch is to display the time. Many watches also display the date and other information. A smartwatch is a small computer worn on a band around the wrist. Smartwatches can perform such functions as sending and receiving text messages, tracking a user’s location, and measuring a user’s physical fitness activity. This article primarily discusses mechanical and electronic watches.
Watches are often considered to be jewelry. Sometimes watches are valued more for their beauty and fashion than for their timekeeping ability. Hundreds of millions of watches are sold each year around the world. Some watches cost less than $10. Others are made from precious metals and set with gemstones, costing hundreds of thousands of dollars.
How watches work
Watches generally display time in one of two ways: analog and digital. An analog watch shows time using hands. The hands point to numbers or markers around the watch’s face. Separate hands display the passage of hours, minutes, and seconds. A digital watch displays the time as a row of numbers.
Watches tell time by counting some regularly repeating action. This action is performed by an oscillator, also called a time base. For example, a mechanical watch might contain a wheel that swings back and forth over and over, five times per second. The swinging wheel functions as the watch’s oscillator. Since the frequency (rate) of the wheel’s swinging is known, the watch’s second hand is designed to tick once for every five swings. Nearly all mechanical watches use an analog display.
Most modern watches are electronic. They use the vibrations of a mineral called quartz as a time base. Quartz watches may use either analog or digital displays. Some quartz watches include both types of displays.
Mechanical watches
are less common than quartz watches, largely because they are costlier and less accurate. However, many people still prefer mechanical watches for their appearance and craftsmanship.
Mechanical watches can have more than 100 moving parts. A coiled spring called a mainspring powers the parts’ movement. A complex mechanism called the escapement regulates how fast the watch’s hands turn.
The mainspring
stores energy. In some mechanical watches, the mainspring must be wound by turning a knob, or crown. Others are self-winding. They contain a weight mechanism that winds the mainspring automatically whenever the watch is moved.
Winding the mainspring supplies it with energy, which it releases as it unwinds. This energy turns several tiny gear wheels. The wheels are connected in a series called the train. The hands of a watch are attached to individual gear wheels that turn at specific speeds. The speed of the gear wheels—and the hands connected to them—is partially determined by the escapement.
The escapement
includes four main parts. They are (1) an escape wheel, (2) a balance wheel, (3) a balance spring, and (4) a pallet lever.
The escape wheel is connected to the train. It turns when the watch runs.
The balance wheel gets energy from the escape wheel. It functions as the watch’s oscillator, typically swinging back and forth five times per second.
The balance spring is also called the hairspring. It makes the balance wheel swing back and forth.
The pallet lever has two pallets (hooks)—one at either end—that catch on the escape wheel. Each swing of the balance wheel causes the pallet lever to swing as well. In the process, the escape wheel briefly escapes the grip of the pallets. The escape wheel then turns slightly before the pallets again catch on it. This catching action stops the movement of the escape wheel and also produces the characteristic ticking of a mechanical watch.
The accuracy of a mechanical watch depends upon the frequency of the balance wheel, because the balance wheel regulates the speed of the escape wheel. Most mechanical watches are only accurate to about 10 to 15 seconds per day. The most sophisticated models can keep time to within a few seconds per day.
Quartz watches
are electronic instruments that are powered by a battery or solar cell. The time base for a quartz watch is a tiny quartz crystal that is often shaped like a tuning fork. The crystal in most quartz watches vibrates 32,768 times per second when electric current is applied. This frequency is too high for a human ear to detect. As a result, a quartz watch does not tick.
A quartz watch’s frequency is equal to 215—that is, 2 multiplied by itself 14 times—vibrations per second. A tiny computerlike device counts the vibrations. Since computers process information based on 2’s, a quartz watch’s frequency is convenient to count. Every 32,768 vibrations—in other words, every second—the counting device generates a signal called a pulse.
In an analog quartz watch, the one pulse per second signal is used to activate a tiny motor, sometimes called a stepping motor, that moves the second hand. Seconds are then counted to accumulate minutes and hours. Digital quartz watches have no moving parts. Instead, the time information goes directly to a liquid crystal display (LCD) on the watch face. An LCD consists of a thin layer of liquid crystal sandwiched between two layers of glass. Numbers are printed onto the glass with transparent conductive coatings. These numbers become visible when an electric charge is applied to the coatings. An LCD display uses little battery power, but it is sometimes hard to see in dim light. For this reason, many LCD watches have a light that can be turned on to illuminate the face.
Most quartz watches are accurate to about 15 seconds per month, which means that they need to be set much less often than mechanical watches. However, quartz watches are sensitive to temperature changes, and they will become less accurate in extremely hot or cold places. The best quartz watches are designed to compensate for temperature changes. They often have oscillators that run at higher frequencies than 32,768 vibrations per second. The highest quality quartz watches are accurate to within 10 seconds per year.
A small percentage of quartz watches are radio controlled. They typically receive a signal broadcast by a government agency that is responsible for keeping the national time standard. This radio signal is used to set the watch automatically so that it is always accurate to within less than 1 second. Most radio controlled watches in the United States receive signals broadcast by the National Institute of Standards and Technology (NIST) from Fort Collins, Colorado.
History
No single person invented the watch. Instead, watches developed alongside other timepieces in the history of clockmaking. The first portable clocks probably appeared during the 1400’s. As clocks continued to get smaller, it eventually became practical for people to carry them around. The word watch possibly came from town watchmen in Europe. They began carrying portable clocks on straps hanging from their necks or belts during the 1500’s.
Early watches were much larger and heavier than today’s models. They kept time so poorly that they only displayed hours, not minutes and seconds. By the late 1600’s, most watches displayed minutes. But watches that displayed seconds did not become common until the 1900’s.
During the late 1600’s, watches became small and light enough to fit into a jacket or vest pocket. These pocket watches were the most popular style of watch for more than 200 years. Wrist watches became more common in the 1800’s. They were originally designed for women only. In the late 1800’s and during World War I (1914-1918), soldiers realized that wrist watches were more convenient than pocket watches. Wrist watches soon became common accessories for men.
Several major advances in watches occurred during the second half of the 1900’s. Quartz watches were first sold to the public in 1969, followed by digital watches in 1972. In the 1970’s, such watchmakers as Seiko and Casio began making watches that used simple computers to store information, function as calculators, and play games. Radio controlled watches were first sold to the public in 1990. Modern smartwatches started growing in popularity in the 2010’s.
