Analysers are used in electrical measuring equipment, particularly in circuit development and as test equipment during production. For example, spectrum analysers show a signal in the frequency range on their build in screens. This can show the quality of signal for mobile applications. They are equipped with numerous interfaces, such as a USB and a printer connection, so data can be saved, printed and evaluated. Power line analysers are also well equipped. They are used for continuous monitoring of voltage quality. They can be used to analyse faults in networks or as a test tool. Function generators periodically produce electrical signals that are used to check circuits. For example, they can be used to check the functioning of amplifiers and filters.