The 7709 is a two-pole 6 x 8 matrix plug-in module which can be any combination of six differential channels or eight differential channels. The instruments can be AC or DC sources as well as internal or external counters, or oscilloscopes. This matrix configuration allows great flexibility for complex test systems. The CLOSE command connects channels 1 to 8 with DMM. With 4-wire, channels 1 to 4 are automatically coupled to channels 13 to 16.