# Analog

An analog system is a mathematical system in which numbers vary continuously instead of shifting between discrete states as a digital system does. For example, in an analog clock, the hour, minute, and second hands all move continuously. Halfway between 2:00 and 3:00, the hour hand will be pointing halfway between the 2 and the 3. In a digital clock, the numbers simply shift between discrete states: halfway between 2:00 and 3:00, the hour digit will still read 2.

A slide rule is an analog calculator whereas an abacus is a digital calculator because the slide rule's numbers vary continuously whereas the abacus' numbers are either all the way up or all the way down, there is no meaning for a bead on an abacus that is half way up or down. Analog televisions are operated by machinery where the numbers vary continuously, whereas in digital television the numbers shift between discrete states; this is also true of analog computers and digital computers.

The need to make fine measurements when reading analog devices severely limits their practical accuracy, and digital devices are usually much more accurate in practice.