diff --git a/vna_qt/mainwindow.C b/vna_qt/mainwindow.C
index 98329ca..3028e81 100644
--- a/vna_qt/mainwindow.C
+++ b/vna_qt/mainwindow.C
@@ -383,8 +383,7 @@ void MainWindow::updatePortExtension() {
     ui->t_ext1->setText(qs(ssprintf(32, "%.0f ps", round(portExt1Seconds*1e12))));
     ui->t_ext2->setText(qs(ssprintf(32, "%.0f ps", round(portExt2Seconds*1e12))));
     ui->t_extz->setText(qs(ssprintf(32, "%.2f", portExtZ0)));
-    for(int i=0;i<vna->nPoints;i++)
-        updateViews(i);
+    updateViews(-1);
 }
 
 static string calFileVer = "calFileVersion 1";
@@ -748,6 +747,22 @@ complex<double> calculatePortExt(complex<double> refl, complex<double> Tcable, d
 }
 
 void MainWindow::updateViews(int freqIndex) {
+    computeViews(freqIndex);
+    if(ui->actionDisable_chart_update->isChecked()) return;
+    nv.updateViews(freqIndex);
+
+    time_t t = time(nullptr);
+    if(abs(int64_t(t) - int64_t(lastDTFUpdate)) >= 1)
+        dtf.updateValues(nv.values);
+    lastDTFUpdate = t;
+}
+
+void MainWindow::computeViews(int freqIndex) {
+    if(freqIndex < 0) {
+        for(int i=0; i<vna->nPoints; i++)
+            computeViews(i);
+        return;
+    }
     if(freqIndex >= (int)nv.values.size()) return;
     if(curCal)
         nv.values.at(freqIndex) = curCal->computeValue(curCalCoeffs.at(freqIndex), this->rawValues.at(freqIndex));
@@ -766,14 +781,6 @@ void MainWindow::updateViews(int freqIndex) {
     nv.values.at(freqIndex)(1, 0) *= polar(1., 2*M_PI*freqHz*(portExt1Seconds+portExt2Seconds));
     // S12
     nv.values.at(freqIndex)(0, 1) *= polar(1., 2*M_PI*freqHz*(portExt1Seconds+portExt2Seconds));
-
-    if(ui->actionDisable_chart_update->isChecked()) return;
-    nv.updateViews(freqIndex);
-
-    time_t t = time(nullptr);
-    if(abs(int64_t(t) - int64_t(lastDTFUpdate)) >= 1)
-        dtf.updateValues(nv.values);
-    lastDTFUpdate = t;
 }
 
 void MainWindow::on_actionLoad_triggered() {
@@ -1039,8 +1046,8 @@ void MainWindow::on_actionFine_tune_triggered() {
     dialog.modelsChanged = [&]() {
         for(int i=0; i<vna->nPoints; i++) {
             curCalCoeffs.at(i) = curCal->computeCoefficients(curCalMeasurementsArray.at(i), dialog.newModels.at(i));
-            updateViews(i);
         }
+        updateViews(-1);
     };
     if(dialog.exec() == QDialog::Accepted) {
         curCalStdModelsArray = dialog.newModels;
diff --git a/vna_qt/mainwindow.H b/vna_qt/mainwindow.H
index 37c0a7c..0f4cb47 100644
--- a/vna_qt/mainwindow.H
+++ b/vna_qt/mainwindow.H
@@ -179,6 +179,9 @@ private slots:
     // update a single point on all views in this->views
     void updateViews(int freqIndex);
 
+    // compute calibrated values but do not refresh widgets; called by updateViews()
+    void computeViews(int freqIndex);
+
     // called when the vna background thread encounters an error
     void handleBackgroundError(QString msg);
 
diff --git a/vna_qt/networkview.C b/vna_qt/networkview.C
index b057164..87f27d0 100644
--- a/vna_qt/networkview.C
+++ b/vna_qt/networkview.C
@@ -191,104 +191,36 @@ void NetworkView::updateViews(int freqIndex) {
 }
 
 void NetworkView::updateView(int viewIndex, int freqIndex) {
-    double period = 1./xAxisStep;
-    double grpDelayScale = period/(2*M_PI) * 1e3;
+    SParamView tmp = this->views.at(viewIndex);
 
+    // if we are updating all frequencies, compute and replace entire chart at once
     if(freqIndex < 0) {
-        for(int i=0;i<(int)values.size();i++) {
-            updateView(viewIndex,i);
+        int sz = (int) values.size();
+        if(tmp.src.type != SParamViewSource::TYPE_COMPLEX) {
+            auto* series = dynamic_cast<QLineSeries*>(tmp.view);
+            QVector<QPointF> pts(sz);
+            for(int i=0; i<sz; i++) {
+                pts[i] = _computeChartPoint(viewIndex, i);
+            }
+            series->replace(pts);
+        } else {
+            for(int i=0; i<sz; i++)
+                updateView(viewIndex, i);
         }
         return;
     }
-    double freqHz = xAxisAt(freqIndex)*1e6; // only meaningful in frequency domain
-    SParamView tmp = this->views.at(viewIndex);
-
     VNACalibratedValue val = this->values.at(freqIndex);
     complex<double> entry = val(tmp.src.row,tmp.src.col);
-    double z0 = 50;
-    complex<double> Z = -z0*(entry+1.)/(entry-1.);
-    complex<double> Y = -(entry-1.)/(z0*(entry+1.));
 
     if(tmp.src.type == SParamViewSource::TYPE_COMPLEX) {
+        // smith chart view
         auto* view = dynamic_cast<PolarView*>(tmp.view);
         view->points.at(freqIndex) = entry;
     } else {
+        // line chart view
         auto* series = dynamic_cast<QLineSeries*>(tmp.view);
-        double y = 0;
-        switch(tmp.src.type) {
-        case SParamViewSource::TYPE_MAG:
-            y = dB(norm(entry));
-            break;
-        case SParamViewSource::TYPE_SWR:
-            y = swr(norm(entry));
-            break;
-        case SParamViewSource::TYPE_PHASE:
-            y = arg(entry)*180./M_PI;
-            break;
-        case SParamViewSource::TYPE_Z_RE:
-            y = Z.real();
-            break;
-        case SParamViewSource::TYPE_Z_IM:
-            y = Z.imag();
-            break;
-        case SParamViewSource::TYPE_Z_MAG:
-            y = abs(Z);
-            break;
-        case SParamViewSource::TYPE_Z_CAP: // capacitance in pF
-            y = -capacitance_inductance(freqHz, Z.imag()) * 1e12;
-            break;
-        case SParamViewSource::TYPE_Z_IND: // inductance in nH
-            y = capacitance_inductance(freqHz, Z.imag()) * 1e9;
-            break;
-        case SParamViewSource::TYPE_Y_RE:
-            y = Y.real() * 1000;
-            break;
-        case SParamViewSource::TYPE_Y_IM:
-            y = Y.imag() * 1000;
-            break;
-        case SParamViewSource::TYPE_Y_MAG:
-            y = abs(Y) * 1000;
-            break;
-        case SParamViewSource::TYPE_Y_CAP: // capacitance in pF
-            y = -capacitance_inductance_Y(freqHz, Y.imag()) * 1e12;
-            break;
-        case SParamViewSource::TYPE_Y_IND: // inductance in nH
-            y = capacitance_inductance_Y(freqHz, Y.imag()) * 1e9;
-            break;
-        case SParamViewSource::TYPE_GRPDELAY:
-        {
-            if(freqIndex>0) {
-                VNACalibratedValue prevVal = this->values.at(freqIndex-1);
-                complex<double> prevEntry = prevVal(tmp.src.row,tmp.src.col);
-                y = arg(prevEntry) - arg(entry);
-                if(y>=M_PI) y-=2*M_PI;
-                if(y<-M_PI) y+=2*M_PI;
-            } else y=0;
-            y *= grpDelayScale;
-            break;
-        }
-        default: assert(false);
-        }
-
-        // clamp values to avoid enlarging labels
-        switch(tmp.src.type) {
-            case SParamViewSource::TYPE_Z_CAP:
-            case SParamViewSource::TYPE_Z_IND:
-            case SParamViewSource::TYPE_Y_CAP:
-            case SParamViewSource::TYPE_Y_IND:
-                if(y < 0) y = 0;
-                if(y > 999) y = 999;
-                break;
-            case SParamViewSource::TYPE_Z_RE:
-            case SParamViewSource::TYPE_Z_IM:
-            case SParamViewSource::TYPE_Z_MAG:
-                if(y < -999) y = -999;
-                if(y > 999) y = 999;
-                break;
-            default: break;
-        }
-
-        series->replace(freqIndex,series->at(freqIndex).x(), y);
+        QPointF pt = _computeChartPoint(viewIndex, freqIndex);
+        series->replace(freqIndex,pt);
     }
 }
 
@@ -434,3 +366,90 @@ int NetworkView::addMarker(bool removable) {
     return newId;
 }
 
+QPointF NetworkView::_computeChartPoint(int viewIndex, int freqIndex) {
+    double period = 1./xAxisStep;
+    double grpDelayScale = period/(2*M_PI) * 1e3;
+    SParamView tmp = this->views.at(viewIndex);
+
+    VNACalibratedValue val = this->values.at(freqIndex);
+    complex<double> entry = val(tmp.src.row,tmp.src.col);
+    double z0 = 50;
+    complex<double> Z = -z0*(entry+1.)/(entry-1.);
+    complex<double> Y = -(entry-1.)/(z0*(entry+1.));
+    double y = 0;
+    double freqHz = xAxisAt(freqIndex)*1e6; // only meaningful in frequency domain
+    switch(tmp.src.type) {
+    case SParamViewSource::TYPE_MAG:
+        y = dB(norm(entry));
+        break;
+    case SParamViewSource::TYPE_SWR:
+        y = swr(norm(entry));
+        break;
+    case SParamViewSource::TYPE_PHASE:
+        y = arg(entry)*180./M_PI;
+        break;
+    case SParamViewSource::TYPE_Z_RE:
+        y = Z.real();
+        break;
+    case SParamViewSource::TYPE_Z_IM:
+        y = Z.imag();
+        break;
+    case SParamViewSource::TYPE_Z_MAG:
+        y = abs(Z);
+        break;
+    case SParamViewSource::TYPE_Z_CAP: // capacitance in pF
+        y = -capacitance_inductance(freqHz, Z.imag()) * 1e12;
+        break;
+    case SParamViewSource::TYPE_Z_IND: // inductance in nH
+        y = capacitance_inductance(freqHz, Z.imag()) * 1e9;
+        break;
+    case SParamViewSource::TYPE_Y_RE:
+        y = Y.real() * 1000;
+        break;
+    case SParamViewSource::TYPE_Y_IM:
+        y = Y.imag() * 1000;
+        break;
+    case SParamViewSource::TYPE_Y_MAG:
+        y = abs(Y) * 1000;
+        break;
+    case SParamViewSource::TYPE_Y_CAP: // capacitance in pF
+        y = -capacitance_inductance_Y(freqHz, Y.imag()) * 1e12;
+        break;
+    case SParamViewSource::TYPE_Y_IND: // inductance in nH
+        y = capacitance_inductance_Y(freqHz, Y.imag()) * 1e9;
+        break;
+    case SParamViewSource::TYPE_GRPDELAY:
+    {
+        if(freqIndex>0) {
+            VNACalibratedValue prevVal = this->values.at(freqIndex-1);
+            complex<double> prevEntry = prevVal(tmp.src.row,tmp.src.col);
+            y = arg(prevEntry) - arg(entry);
+            if(y>=M_PI) y-=2*M_PI;
+            if(y<-M_PI) y+=2*M_PI;
+        } else y=0;
+        y *= grpDelayScale;
+        break;
+    }
+    default: assert(false);
+    }
+
+    // clamp values to avoid enlarging labels
+    switch(tmp.src.type) {
+        case SParamViewSource::TYPE_Z_CAP:
+        case SParamViewSource::TYPE_Z_IND:
+        case SParamViewSource::TYPE_Y_CAP:
+        case SParamViewSource::TYPE_Y_IND:
+            if(y < 0) y = 0;
+            if(y > 999) y = 999;
+            break;
+        case SParamViewSource::TYPE_Z_RE:
+        case SParamViewSource::TYPE_Z_IM:
+        case SParamViewSource::TYPE_Z_MAG:
+            if(y < -999) y = -999;
+            if(y > 999) y = 999;
+            break;
+        default: break;
+    }
+    return QPointF(xAxisAt(freqIndex), y);
+}
+
diff --git a/vna_qt/networkview.H b/vna_qt/networkview.H
index 607b0f8..3524fc6 100644
--- a/vna_qt/networkview.H
+++ b/vna_qt/networkview.H
@@ -117,6 +117,8 @@ public:
     void updateBottomLabels(int marker=-1);
     void updateYAxis(int viewIndex=-1);
     int addMarker(bool removable);
+
+    QPointF _computeChartPoint(int viewIndex, int freqIndex);
 signals:
     void markerChanged(int marker, int newIndex);
 };