Base components are the required components of the ActiveTwo system, and these items are typically included in the fundamental building block of each system known as the Base System.  The Base System includes an A/D interface box with no channels installed, USB 2.0 interface box with USB 2.0 cable, two rechargeable battery units, battery charger with A/C adapter and the ActiView data acquisition software.  Channels are added to the base system by inserting 8 channel amplifier/converter modules, which are not part of the Base System.  In the event you are upgrading a system, you need a spare or replacement component or you are building a custom system configuration, these individual components may be ordered separately.