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Analog device is usually a combination of both analog machine and analog media that can together measure, record, or reproduce (emit[disambiguation needed]) continuous information, for example, the almost infinite number of grades of transparency, voltage, resistance, rotation, or pressure. In theory, the continuous information (also analog signal) has an infinite number of possible values with the only limitation on resolution being the accuracy of the analog device.
There are notable non-electrical analog devices, such as clocks (sundials, water clocks, pendulum clocks, analog watches), the astrolabe, slide rules, the governor of a steam engine, the planimeter (a simple device that measures the area of a closed shape), Kelvin's mechanical tide predictor, acoustic rangefinders, servomechanisms (e.g. the thermostat), a simple mercury thermometer, a bathroom scale, and the speedometer of a car.
The telautograph is an analogue precursor to the modern fax machine. Basically it transmits electrical impulses recorded by potentiometers to stepping motors attached to a pen, thus being able to reproduce a drawing or signature made by the sender at the receiver's station. It was the first such device to transmit drawings to a stationary sheet of paper; previous inventions in Europe used rotating drums to make such transmissions.
The analog television encodes television and transports the picture and sound information as an analogue signal, that is, by varying the amplitude and/or frequencies of the broadcast signal. All systems preceding digital television, such as NTSC, PAL or UNIT are analog television systems.
An analog computer is a form of computer that uses electrical, mechanical or hydraulic phenomena to model the problem being solved. More generally an analog computer uses one kind of physical quantity to represent the behaviour of another physical system, or mathematical function. Modeling a real physical system in a computer is called simulation.
Interfacing the digital and analog worlds
In electronics, a digital-to-analog converter (DAC or D-to-A) is a circuit for converting a digital signal (usually binary) to an analog signal (current, voltage or electric charge). Digital-to-analog converters are interfaces between the digital world and analog world. An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic circuit that converts continuous signals to discrete digital numbers.
Controversy over photographic film
There is quite a bit of controversy in the photographic world as to whether or not a film camera should be considered an "analog device" since the photographic film isn't a truly analog recording medium and requires chemistry to process an image. "Analog" has become the common term for referring to cameras that are "not digital" and is an easy shorthand for people to differentiate between the two mediums.