I have done 1-port calibration (50MHz to 18GHz) with 8510C using 85054D end of the test port cable. When I'm measuring another 85054D calkit Open and Shorts reflection coefficient following quite nicely calculated Open and shorts polynomical reflection coefficients. If I'm repeating the same calibration and measurements with 8720 series analyzers, Open and short results showing slightly over 1 reflection coefficient values on some part of the sweep (standard definitions are exatly the same on 8510C and 8720). Where this difference might come? When I'm comparing 8510C and 8720 open and short results together, phase values showing almost the same value. Only the magnitude values has difference. All used analyzers are well factory calibrated and meet spesifications, so instruments are good shape.