diff --git a/Software/PC_Application/Calibration/calkit.cpp b/Software/PC_Application/Calibration/calkit.cpp
index d02dd58..3fa14b5 100644
--- a/Software/PC_Application/Calibration/calkit.cpp
+++ b/Software/PC_Application/Calibration/calkit.cpp
@@ -90,6 +90,11 @@ Calkit Calkit::fromFile(QString filename)
         throw runtime_error("JSON parsing error: " + string(e.what()));
     }
     if(j.contains("SOLT")) {
+        // older file versions specify Z0 for resistance. If resistance entry is missing,
+        // set it to Z0 later
+        bool loadResistanceMissing_m = false;
+        bool loadResistanceMissing_f = false;
+
         qDebug() << "JSON format detected";
         // calkit file uses json format, parse
         for(auto e : c.json_descr) {
@@ -108,6 +113,11 @@ Calkit Calkit::fromFile(QString filename)
             if(!entry_exists) {
                 // missing entry in json file, nothing to do (default values already set in constructor)
                 qWarning() << "Entry" << e.name << "not present in file, assuming default value";
+                if(e.name == "SOLT/Load/Param/Resistance") {
+                    loadResistanceMissing_m = true;
+                } else if(e.name == "SOLT/Load/Param/Resistance_Female") {
+                    loadResistanceMissing_f = true;
+                }
                 continue;
             }
             // json library does not now about QVariant, handle used cases
@@ -126,6 +136,15 @@ Calkit Calkit::fromFile(QString filename)
                 throw runtime_error("Unimplemented metatype");
             }
         }
+        // adjust Z0/resistance in case of older calkit file version
+        if(loadResistanceMissing_f) {
+            c.SOLT.load_f.resistance = c.SOLT.load_f.Z0;
+            c.SOLT.load_f.Z0 = 50.0;
+        }
+        if(loadResistanceMissing_m) {
+            c.SOLT.load_m.resistance = c.SOLT.load_m.Z0;
+            c.SOLT.load_m.Z0 = 50.0;
+        }
     } else {
         qDebug() << "Legacy format detected";
         // legacy file format, return to beginning of file
@@ -149,7 +168,7 @@ Calkit Calkit::fromFile(QString filename)
         c.SOLT.short_m.L1 = readLine(file).toDouble();
         c.SOLT.short_m.L2 = readLine(file).toDouble();
         c.SOLT.short_m.L3 = readLine(file).toDouble();
-        c.SOLT.load_m.Z0 = readLine(file).toDouble();
+        c.SOLT.load_m.resistance = readLine(file).toDouble();
         c.SOLT.Through.Z0 = readLine(file).toDouble();
         c.SOLT.Through.delay = readLine(file).toDouble();
         c.SOLT.Through.loss = readLine(file).toDouble();
@@ -243,7 +262,7 @@ class Calkit::SOLT Calkit::toSOLT(double frequency, bool male_standards)
     if(Load.useMeasurements) {
         ref.Load = ts_load->interpolate(frequency).S[0];
     } else {
-        auto imp_load = complex<double>(Load.Z0, 0);
+        auto imp_load = complex<double>(Load.resistance, 0);
         // Add parallel capacitor to impedance
         if(Load.Cparallel > 0) {
             auto imp_C = complex<double>(0, -1.0 / (frequency * 2 * M_PI * Load.Cparallel));
@@ -253,7 +272,7 @@ class Calkit::SOLT Calkit::toSOLT(double frequency, bool male_standards)
         auto imp_L = complex<double>(0, frequency * 2 * M_PI * Load.Lseries);
         imp_load += imp_L;
         ref.Load = (imp_load - complex<double>(50.0)) / (imp_load + complex<double>(50.0));
-        ref.Load = addTransmissionLine(ref.Load, 50.0, Load.delay*1e-12, 0, frequency);
+        ref.Load = addTransmissionLine(ref.Load, Load.Z0, Load.delay*1e-12, 0, frequency);
     }
 
     if(Open.useMeasurements) {
diff --git a/Software/PC_Application/Calibration/calkit.h b/Software/PC_Application/Calibration/calkit.h
index 5502cf9..8e3fc85 100644
--- a/Software/PC_Application/Calibration/calkit.h
+++ b/Software/PC_Application/Calibration/calkit.h
@@ -73,7 +73,7 @@ private:
         };
         Short short_m, short_f;
         using Load = struct {
-            double Z0, delay, Cparallel, Lseries;
+            double resistance, Z0, delay, Cparallel, Lseries;
             QString file;
             bool useMeasurements;
             int Sparam;
@@ -110,7 +110,7 @@ private:
         QString name;
         QVariant def;
     };
-    const std::array<JSONDescription, 71> json_descr = {{
+    const std::array<JSONDescription, 73> json_descr = {{
         {&manufacturer, "Manufacturer", ""},
         {&serialnumber, "Serialnumber", ""},
         {&description, "Description", ""},
@@ -157,6 +157,7 @@ private:
         {&SOLT.short_f.file, "SOLT/Short/Measurements/File_Female", ""},
         {&SOLT.short_f.Sparam, "SOLT/Short/Measurements/Port_Female", 0},
 
+        {&SOLT.load_m.resistance, "SOLT/Load/Param/Resistance", 50.0},
         {&SOLT.load_m.Z0, "SOLT/Load/Param/Z0", 50.0},
         {&SOLT.load_m.delay, "SOLT/Load/Param/Delay", 0.0},
         {&SOLT.load_m.Cparallel, "SOLT/Load/Param/C", 0.0},
@@ -164,6 +165,7 @@ private:
         {&SOLT.load_m.useMeasurements, "SOLT/Load/Measurements/Use", false},
         {&SOLT.load_m.file, "SOLT/Load/Measurements/File", ""},
         {&SOLT.load_m.Sparam, "SOLT/Load/Measurements/Port", 0},
+        {&SOLT.load_f.resistance, "SOLT/Load/Param/Resistance_Female", 50.0},
         {&SOLT.load_f.Z0, "SOLT/Load/Param/Z0_Female", 50.0},
         {&SOLT.load_f.delay, "SOLT/Load/Param/Delay_Female", 0.0},
         {&SOLT.load_f.Cparallel, "SOLT/Load/Param/C_Female", 0.0},
diff --git a/Software/PC_Application/Calibration/calkitdialog.cpp b/Software/PC_Application/Calibration/calkitdialog.cpp
index cd84de7..6d66a62 100644
--- a/Software/PC_Application/Calibration/calkitdialog.cpp
+++ b/Software/PC_Application/Calibration/calkitdialog.cpp
@@ -42,6 +42,7 @@ CalkitDialog::CalkitDialog(Calkit &c, QWidget *parent) :
 
     ui->short_Z0->setUnit("Ω");
     ui->open_Z0->setUnit("Ω");
+    ui->load_resistance->setUnit("Ω");
     ui->load_Z0->setUnit("Ω");
     ui->load_parC->setUnit("F");
     ui->load_parC->setPrefixes("fpnum ");
@@ -64,6 +65,7 @@ CalkitDialog::CalkitDialog(Calkit &c, QWidget *parent) :
 
     ui->short_Z0_f->setUnit("Ω");
     ui->open_Z0_f->setUnit("Ω");
+    ui->load_resistance_f->setUnit("Ω");
     ui->load_Z0_f->setUnit("Ω");
     ui->load_parC_f->setUnit("F");
     ui->load_parC_f->setPrefixes("fpnum ");
@@ -247,6 +249,7 @@ void CalkitDialog::parseEntries()
     ownKit.SOLT.short_m.L2 = ui->short_L2->value();
     ownKit.SOLT.short_m.L3 = ui->short_L3->value();
 
+    ownKit.SOLT.load_m.resistance = ui->load_resistance->value();
     ownKit.SOLT.load_m.Z0 = ui->load_Z0->value();
     ownKit.SOLT.load_m.delay = ui->load_delay->value();
     ownKit.SOLT.load_m.Cparallel = ui->load_parC->value();
@@ -268,6 +271,7 @@ void CalkitDialog::parseEntries()
     ownKit.SOLT.short_f.L2 = ui->short_L2_f->value();
     ownKit.SOLT.short_f.L3 = ui->short_L3_f->value();
 
+    ownKit.SOLT.load_f.resistance = ui->load_resistance_f->value();
     ownKit.SOLT.load_f.Z0 = ui->load_Z0_f->value();
     ownKit.SOLT.load_f.delay = ui->load_delay_f->value();
     ownKit.SOLT.load_f.Cparallel = ui->load_parC_f->value();
@@ -332,6 +336,7 @@ void CalkitDialog::updateEntries()
     ui->short_L2->setValueQuiet(ownKit.SOLT.short_m.L2);
     ui->short_L3->setValueQuiet(ownKit.SOLT.short_m.L3);
 
+    ui->load_resistance->setValueQuiet(ownKit.SOLT.load_m.resistance);
     ui->load_Z0->setValueQuiet(ownKit.SOLT.load_m.Z0);
     ui->load_delay->setValueQuiet(ownKit.SOLT.load_m.delay);
     ui->load_parC->setValueQuiet(ownKit.SOLT.load_m.Cparallel);
@@ -353,6 +358,7 @@ void CalkitDialog::updateEntries()
     ui->short_L2_f->setValueQuiet(ownKit.SOLT.short_f.L2);
     ui->short_L3_f->setValueQuiet(ownKit.SOLT.short_f.L3);
 
+    ui->load_resistance_f->setValueQuiet(ownKit.SOLT.load_f.resistance);
     ui->load_Z0_f->setValueQuiet(ownKit.SOLT.load_f.Z0);
     ui->load_delay_f->setValueQuiet(ownKit.SOLT.load_f.delay);
     ui->load_parC_f->setValueQuiet(ownKit.SOLT.load_f.Cparallel);
diff --git a/Software/PC_Application/Calibration/calkitdialog.ui b/Software/PC_Application/Calibration/calkitdialog.ui
index bef6c3d..3cb705d 100644
--- a/Software/PC_Application/Calibration/calkitdialog.ui
+++ b/Software/PC_Application/Calibration/calkitdialog.ui
@@ -722,7 +722,7 @@
                <item>
                 <widget class="QTabWidget" name="mf_load">
                  <property name="currentIndex">
-                  <number>0</number>
+                  <number>1</number>
                  </property>
                  <widget class="QWidget" name="tab_7">
                   <attribute name="title">
@@ -762,50 +762,60 @@
                       <layout class="QHBoxLayout" name="horizontalLayout_10">
                        <item>
                         <layout class="QFormLayout" name="formLayout_3">
-                         <item row="0" column="0">
+                         <item row="1" column="0">
                           <widget class="QLabel" name="label_30">
                            <property name="text">
                             <string>Z0:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="0" column="1">
+                         <item row="1" column="1">
                           <widget class="SIUnitEdit" name="load_Z0">
                            <property name="enabled">
                             <bool>true</bool>
                            </property>
                           </widget>
                          </item>
-                         <item row="1" column="0">
+                         <item row="2" column="0">
                           <widget class="QLabel" name="label_17">
                            <property name="text">
                             <string>Offset delay [ps]:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="1" column="1">
+                         <item row="2" column="1">
                           <widget class="SIUnitEdit" name="load_delay"/>
                          </item>
-                         <item row="2" column="0">
+                         <item row="3" column="0">
                           <widget class="QLabel" name="label_18">
                            <property name="text">
                             <string>Parallel C:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="2" column="1">
+                         <item row="3" column="1">
                           <widget class="SIUnitEdit" name="load_parC"/>
                          </item>
-                         <item row="3" column="0">
+                         <item row="4" column="0">
                           <widget class="QLabel" name="label_26">
                            <property name="text">
                             <string>Series L:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="3" column="1">
+                         <item row="4" column="1">
                           <widget class="SIUnitEdit" name="load_serL"/>
                          </item>
+                         <item row="0" column="0">
+                          <widget class="QLabel" name="label_29">
+                           <property name="text">
+                            <string>Resistance:</string>
+                           </property>
+                          </widget>
+                         </item>
+                         <item row="0" column="1">
+                          <widget class="SIUnitEdit" name="load_resistance"/>
+                         </item>
                         </layout>
                        </item>
                       </layout>
@@ -859,50 +869,60 @@
                       <layout class="QVBoxLayout" name="verticalLayout_3">
                        <item>
                         <layout class="QFormLayout" name="formLayout_12">
-                         <item row="0" column="0">
+                         <item row="1" column="0">
                           <widget class="QLabel" name="label_61">
                            <property name="text">
                             <string>Z0:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="0" column="1">
+                         <item row="1" column="1">
                           <widget class="SIUnitEdit" name="load_Z0_f">
                            <property name="enabled">
                             <bool>true</bool>
                            </property>
                           </widget>
                          </item>
-                         <item row="1" column="0">
+                         <item row="2" column="0">
                           <widget class="QLabel" name="label_62">
                            <property name="text">
                             <string>Offset delay [ps]:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="1" column="1">
+                         <item row="2" column="1">
                           <widget class="SIUnitEdit" name="load_delay_f"/>
                          </item>
-                         <item row="2" column="0">
+                         <item row="3" column="0">
                           <widget class="QLabel" name="label_63">
                            <property name="text">
                             <string>Parallel C:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="2" column="1">
+                         <item row="3" column="1">
                           <widget class="SIUnitEdit" name="load_parC_f"/>
                          </item>
-                         <item row="3" column="0">
+                         <item row="4" column="0">
                           <widget class="QLabel" name="label_64">
                            <property name="text">
                             <string>Series L:</string>
                            </property>
                           </widget>
                          </item>
-                         <item row="3" column="1">
+                         <item row="4" column="1">
                           <widget class="SIUnitEdit" name="load_serL_f"/>
                          </item>
+                         <item row="0" column="0">
+                          <widget class="QLabel" name="label_32">
+                           <property name="text">
+                            <string>Resistance:</string>
+                           </property>
+                          </widget>
+                         </item>
+                         <item row="0" column="1">
+                          <widget class="SIUnitEdit" name="load_resistance_f"/>
+                         </item>
                         </layout>
                        </item>
                       </layout>
@@ -1456,12 +1476,12 @@
   </connection>
  </connections>
  <buttongroups>
-  <buttongroup name="ThroughType"/>
-  <buttongroup name="LoadType"/>
   <buttongroup name="LoadType_f"/>
-  <buttongroup name="OpenType_f"/>
-  <buttongroup name="ShortType"/>
   <buttongroup name="OpenType"/>
+  <buttongroup name="LoadType"/>
+  <buttongroup name="ShortType"/>
+  <buttongroup name="ThroughType"/>
+  <buttongroup name="OpenType_f"/>
   <buttongroup name="TRL_Rtype"/>
   <buttongroup name="ShortType_f"/>
  </buttongroups>