This section of IEC 368-2 describes passive band-pass filters operating over the frequency range of a few kHz to more than 10 MHz which are commercially available as separate and independent units. It is not the aim of this standard to explain theory, nor to attempt to cover all the eventualities which may arise in practical circumstances. This standard draws attention to some of the fundamental questions which should be considered by the user before he places an order for a filter for a new application. Such a procedure will be the user's insurance against unsatisfactory performance.