The WR-62 cal kit example from hp app note 8510-5B was entered into an hp 8753D after changing the values to those for WR-284. But, when a Full 2-port calibration was attempted, the "Additional Standards Needed" error message came up after measuring the first standard. Not sure how to troubleshoot this one. The first thing I would like to know is whether this is cockpit error, or a problem with the vna, etc. Everything was done manually, from the front panel.