A watch's movement is quite simply its engine. Watches have one of two kinds of movements these days: quartz or mechanical. A quartz movement is an electronic movement. It is called a quartz movement, because a small quartz crystal is actually integrated into the electronics. Why? Because every timekeeping device needs something constant to measure time against, and when you run a current through a quartz crystal, it oscillates at an almost perfectly constant frequency. This explains the incredible accuracy of many quarts watches. A better quartz watch by a manufacturer such as Seiko may be accurate to within a few seconds a year.
Most quartz watches are battery powered. Batteries generally last two to five years before they need to be changed, otherwise quartz watches are very low maintenance. Watches with fancy features such as electric illumination, compasses or stopwatches may go through batteries more quickly.
Not every quartz watch is battery powered. Citizen employs what they call "Eco-drive technology" which is a fancy way of saying solar powered. Citizen Eco-drive watches charge themselves even with ordinary indoor light and can run up to several months without additional exposure to light when fully charged. Many Casio watches have a similar "tough solar" technology.
Quartz watches are very accurate, less expensive and because they don't have a lot of moving parts, more durable than mechanical watches. They can also be equipped with a lot more features such as those found in high tech watch brands such as Suunto watches. These may include electronic compasses, altimeters, barometers, thermometers, alarms, illumination and even GPS.
Mechanical watches, including automatic, or self-winding and manual-wind mechanicals, after having been rendered obsolete by quartz watches when they were introduced in the late 1960s, have become not-so-obsolete anymore.
Mechanical watches employ old technology, several-hundred-years-old technology. Mechanical watches are powered by springs, which turn gears, a regulating mechanism and eventually the hands. A mechanical movement will have somewhere between 50 and 300 parts, depending on the movement, and are somewhat delicate compared to quartz movements. They will however last a long, long time if properly maintained and cared for.
Fine mechanical watches are often handed down from generation to generation as heirlooms. Their longevity is due in part to the use of jewels in the movement. Jewels, usually synthetic rubies, are used in mechanical movements to reduce the effects of friction at certain points where metal would otherwise rub against metal. Most luxury and fine Swiss made watches such as Rolex watches are mechanical, however, many manufacturers such as Swiss Army Victorinox makes very good quality, but less expensive mechanical watches.
Mechanical watches are either self-winding automatic watches, or manual-wind watches. Automatic watches are the most common type of mechanical watches. An automatic watch has a rotor that spins on the back of the watch's movement much like the Seiko Kinetic watches mentioned above. But in this case, instead of generating a charge, it turns a gear which winds the mainspring.
Functionally, mechanical watches are usually pretty simple: hours, minutes, seconds, date, sometimes day and sometimes a chronograph (stopwatch) feature, although chronographs tend to be more expensive. Much, much more expensive are mechanical watches with features such as alarms, minute repeaters, perpetual calendars and toubillons. These watches, called "complicated watches" commonly sell for up to several hundred thousand dollars.
People who buy mechanical watches are often fascinated by their amazing micro mechanics and ancient technology. In fact, mechanical watches usually have a window on the case back to allow you to observe the movement. Quartz watches are sometimes viewed as throwaway watches, while someone might hang onto a mechanical watch for a lifetime. Good mechanical watches are also pretty accurate, but not as accurate as a quartz watch. A mechanical watch may be accurate to within a few second per day.
Mechanical watches require cleaning and maintenance every few years. This can cost $100 or more, but will help insure that the watch will run for years and years.
The best mechanical watches are Swiss made, although Japanese manufacturers such as Miyota (Citizen) and Seiko also make some very good movements. The majority of Swiss movements are made by one company, called ETA.
So if you are looking for a practical, low-maintenance watch that is always accurate, you may want to look for a quartz watch. Or if you are looking for a lot of gadgetry, you may only find what you are looking for in a quartz watch. But if you are very traditional, looking to start a watch collection, have a fascination with old technology, or are looking for a watch to last a lifetime, a mechanical watch may be right for you.