Today the world of electronics is a mixture of analogue and digital circuitry. Many systems such as amplifiers, radios and televisions operate by using analogue signals. However, other systems such as watches, calculators and computers operate using digital signals. As time passes more and more traditional analogue systems are superseded by digital forms, notably, ni-cam digital stereo, the compact audio disc and audio cassette machines which employ digitally recorded magnetic tape. There is a significant difference between analogue waveforms or signals and those which are considered to be digital. It is a good starting point to establish clearly the difference between the two types of signal.