Some clocks, called 'flip clocks', have digital displays that work mechanically. The digits are painted on sheets of material which are mounted like the pages of a book. Once a minute, a page is turned over to reveal the next digit. These displays are usually easier to read in brightly lit conditions than LCDs or LEDs. Also, they do not go back to 12:00 after a power interruption. Flip clocks generally do not have electronic mechanisms. Usually, they are driven by AC-synchronous motors.
Some predecessors to the modern clock may be considered as "clocks" that are based on movement in nature: A sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, a well-known example being the hourglass. Water clocks, along with the sundials, are possibly the oldest time-measuring instruments. A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.
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A. Like many items today, the amount you’ll pay for an alarm clock depends on how much technology you want layered onto it. If you desire nothing but a simple analog alarm clock that rouses you with a single tone, you could spend as little as $10. A slightly more sophisticated clock radio might cost $20 or so. If you want a deluxe digital alarm clock with screen projection, Bluetooth capability, MP3 player, or other cool features, you’re looking at a price of anywhere from $40 to $90.
Wall clocks are available in a wide array of colors to fit any decor style. Classic black and white, silver or antique metal, and natural, brown, or dark wood choices have timeless appeal. Fun colors like red or turquoise are also available. Most clocks feature a high-contrast face with a white background and black numbers or roman numerals to make seeing the time easier.
Don't worry, Zeus didn't show up to your home, but you'll certainly feel that way when waking up to this unit's thunderous, 113-decibel buzzing. Fair warning: It's definitely loud, so it's a good pick only if you're a heavy, heavy sleeper. Just in case the noise somehow isn't enough to pry you out of bed, this alarm clock flashes multiple bright red LEDs and comes with a bed shaker that'll really get you going. Trust us, if that sensory overload doesn't get the job done, nothing will.
The late Roman statesman Cassiodorus (c. 485–585) advocated in his rulebook for monastic life the water clock as a useful alarm for the 'soldiers of Christ' (Cassiod. Inst. 30.4 f.). The Christian rhetorician Procopius described in detail prior to 529 a complex public striking clock in his home town Gaza which featured an hourly gong and figures moving mechanically day and night.
Most digital computers depend on an internal signal at constant frequency to synchronize processing; this is referred to as a clock signal. (A few research projects are developing CPUs based on asynchronous circuits.) Some equipment, including computers, also maintains time and date for use as required; this is referred to as time-of-day clock, and is distinct from the system clock signal, although possibly based on counting its cycles.
Special features beyond simply keeping time can be either practical or decorative. Often found in the kitchen or other busy room, some digital clocks can show readings of the indoor or outdoor temperature, display the date, and have the capacity to set an alarm or timer. A swinging pendulum is most commonly found on fancier wood and metal clocks, though some novelty styles also feature a pendulum.
In a clock driven by a weight or a spring, the power is first transmitted by the main, or great, wheel. This engages with a pinion (a gear with a small number of teeth designed to mesh with a larger wheel), whose arbor (a turning rod to which gears are attached) is attached to the second wheel that, in its turn, engages with the next pinion, and so on, down through the train to the escapement. The gear ratios are such that one arbor, usually the second or third, rotates once an hour and can be used to carry the minute hand. A simple 12-to-1 gearing, known as the motion work, gives the necessary step-down ratio to drive the hour hand. The spring or weight is fitted with a mechanism so it can be rewound when necessary, and the arbor carrying the minute hand is provided with a simple slipping clutch that allows the hands to be set to the correct time.
“Great alarm clock for the price. Gigantic numbers for my old eyes. Very basic, easy to set, just what I wanted. Alarm is loud even on low [with] an awful sound that would wake the dead. But that sound makes me get right up, so it does exactly what it’s supposed to do. If you want a soft gentle caress to wake you, get something else, but this is a good alarm and easy to use.”