Apple's iWatch is about so much more than just keeping time. Assuming the device amounts to more than just rumor, this device and other smartwatches like it, such as the Pebble or Samsung's Galaxy Gear, are so far removed from simple time-keeping instruments as to almost merit a category of device all their own.

But just how did humans get from telling time from the positioning of the sun to checking the time while reading a text, listening to music and monitoring distance traveled during a jog?

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The sexagemisal system of telling time still in use today was invented by the Sumerians roughly 4,000 years ago. The earliest time-keeping instruments used the positioning of the sun to approximate the hour of the day.

Using the positioning of the sun to tell the time of day has its disadvantages, however. On an overcast day, for example, a sundial is of no use at all.

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The sundial precedes other methods of telling time, but it was later followed by the water clock, which also led to the invention of the first alarm clock. These devices still, however, told time somewhat imprecisely, as the passage of the day could only be measure in hours.

More precise methods of measuring time, such as the candle clock or the hourglass, would soon follow. None of these held much promise of affording a portable method of telling time, at least not until the invention of the first mechanical clock.

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Prior to the invention of the pocket watch, the best time-keeping device available was the mechanical clock, a precise instrument that was first built in the 11th century.

The earliest mechanical clocks were large and built into religious establishments like churches and cathedrals. As mechanical clocks grew more precise, minute and, later, second hands were added. As these clocks were better made, they also got smaller.

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The pocket watch is the arguably first-ever mobile device, as other time-keeping instruments could only remain stationary.

The first pocket watches were made in the 16th century. Although conveniently portable, the earliest models only had hour hands and could be inaccurate. That was the case, at least, until the invention of a balance spring, which serves the same purpose as a pendulum in a larger mechanical clock, in the 17th century.

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Wrist watches were first invented in the 16th century around the same time as pocket watches. Although wrist watches are worn by both sexes today, prior to the 20th century, wrist watches were worn almost exclusively by women, with men favoring pocket watches.

This standard changed in the 19th century. Wrist watches were first adopted by military men as an alternative to pocket watches simply because they were a more convenient time-keeping device. At the end of World War I in the 20th century, public attitudes toward wrist watches as being exclusive to one gender changed.

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Up until the 20th century, wrist watches were still mechanical devices. The first electric wrist watches were produced in the 1950s.

These watches still basically had the same assembly as their mechanical counterparts. They didn't require winding, however, with the movement of the hour, minute and second hands powered by a battery.

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The electric watch didn't last long before being displaced by the more accurate and more easily assembled quartz watch, invented in the early 1960s.

In place of the balance spring to tell time, a quartz crystal within a wrist watch resonates at a fixed frequency when an electrical current passes through. The movement of the crystal is then calculated in order to track the time.

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In 1972, Hamilton released the world's first commercial digital watch. Given that a digital watch can cost under $10 today, it might seem surprising that the first-ever digital watch retailed for $2,100 at the time, which is about $11,400 today, according to PC Magazine.

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Just as Hamilton blazed the trail for the first digital watch, so too did the company create the first calculator watch in the mid-1970s.

An ancestor to the modern smartwatch, the first calculator watches could only perform basic functions and had buttons so small that they could only be pressed with a special stylus sold with the device.

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Although smart watches are a recent innovation, the first watches equipped with a small viewing screen for interactive entertainment was invented in 1982 by Seiko.

Outfitted with a 1.1-inch screen and a much larger TV/FM tuner meant to be worn around the belt, the watch had numerous design flaws, such as the lack of a backlit screen, and was quickly withdrawn from the market.

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In the 1980s and 1990s, additional functions were tacked on to wrist watches, including night lights, portable games and, in the case of this Casio watch, an infrared transmitter to serve as a remote control for TV and video functions.

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The addition of GPS was one of the last major enhancements to wrist watches before the development of full-fledged smart watches. The first GPS watch to reach consumers made it to market in 1999.

Although they can be used for navigation, GPS watches are typically used for sports and fitness purposes, and may include heart-rate monitor, speed/route tracking and other complimentary functions.

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Before every portable phone manufactured had a camera attached to it, Casio attempted to market a wrist watch equipped with a camera that shot 120-by-120-pixel photos. The product, first launched in 2002, proved a failure as phone technology quickly eclipsed the limited photo abilities of this watch.