Analog device

Analog device is an apparatus that measures continuous information. The measured analog signal has an infinite number of possible values. The only limitation on resolution is the accuracy of the measuring device. Such apparatus operates with variables which are constituted by continuously measured quantities. These quantities can be voltage, resistance, rotation and pressure.
Examples

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.

An analog synthesizer is a synthesizer that uses analog circuits and analog computer techniques to generate sound electronically.

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 SECAM 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.

There are also many 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 (eg the thermostat), a simple mercury thermometer, a bathroom scale, and the speedometer of a car.
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. The reverse operation is performed by a digital-to-analog converter (DAC).