Write down the cell constant and change it to 1.00 (this is not mandatory, it makes the math easier)
Place a jumper wire between 13 to 14 and another one on 15 to 16 (not necessary on the DC400/402)
Place a resistance between the 13/14 and 15/16 connection. If the unit is set in resistivity it should match the resistance. If it is displaying conductivity it should read Y where Y = (cell constant)/(input resistance) and the units are Siemens. So if the result is 0.005 Siemens this equals 5 milliSiemens.and 0.000005 Siemens equals 5 microSiemens.
Remember to set the cell constant back to the original value if you changed it.