diff --git a/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp b/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
index 8c0e7ae..957ac6c 100644
--- a/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
@@ -333,6 +333,7 @@ SpectrumAnalyzer::SpectrumAnalyzer(AppWindow *window, QString name)
 
 void SpectrumAnalyzer::deactivate()
 {
+    setOperationPending(false);
     StoreSweepSettings();
     Mode::deactivate();
 }
@@ -503,6 +504,9 @@ void SpectrumAnalyzer::NewDatapoint(DeviceDriver::SAMeasurement m)
     }
 
     auto m_avg = average.process(m);
+    if(average.settled()) {
+        setOperationPending(false);
+    }
 
     if(settings.freqStart == settings.freqStop) {
         // keep track of first point time
@@ -560,6 +564,7 @@ void SpectrumAnalyzer::NewDatapoint(DeviceDriver::SAMeasurement m)
 
 void SpectrumAnalyzer::SettingsChanged()
 {
+    setOperationPending(true);
     configurationTimer.start(100);
     ResetLiveTraces();
 }
@@ -703,6 +708,7 @@ void SpectrumAnalyzer::SetAveraging(unsigned int averages)
     average.setAverages(averages);
     emit averagingChanged(averages);
     UpdateAverageCount();
+    setOperationPending(!average.settled());
 }
 
 void SpectrumAnalyzer::SetTGEnabled(bool enabled)
@@ -887,6 +893,7 @@ void SpectrumAnalyzer::ConfigureDevice()
 
 void SpectrumAnalyzer::ResetLiveTraces()
 {
+    setOperationPending(true);
     average.reset(DeviceDriver::SApoints());
     traceModel.clearLiveData();
     UpdateAverageCount();
diff --git a/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp b/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
index e46eca0..13006f4 100644
--- a/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
@@ -692,6 +692,7 @@ QString VNA::getCalToolTip()
 
 void VNA::deactivate()
 {
+    setOperationPending(false);
     StoreSweepSettings();
     Mode::deactivate();
 }
@@ -901,6 +902,9 @@ void VNA::NewDatapoint(DeviceDriver::VNAMeasurement m)
     }
 
     m_avg = average.process(m_avg);
+    if(average.settled()) {
+        setOperationPending(false);
+    }
 
     if(calMeasuring) {
         if(average.currentSweep() == averages) {
@@ -979,6 +983,7 @@ void VNA::UpdateAverageCount()
 
 void VNA::SettingsChanged(bool resetTraces, int delay)
 {
+    setOperationPending(true);
     configurationTimer.start(delay);
     changingSettings = true;
     configurationTimerResetTraces = resetTraces;
@@ -1218,6 +1223,7 @@ void VNA::SetAveraging(unsigned int averages)
     average.setAverages(averages);
     emit averagingChanged(averages);
     UpdateAverageCount();
+    setOperationPending(!average.settled());
 }
 
 void VNA::ExcitationRequired()
@@ -1317,7 +1323,6 @@ void VNA::SetupSCPI()
         if(params.size() >= 1) {
             if(params[0] == "FREQUENCY") {
                 SetSweepType(SweepType::Frequency);
-                ResetLiveTraces();
                 return SCPI::getResultName(SCPI::Result::Empty);
             } else if(params[0] == "POWER") {
                 SetSweepType(SweepType::Power);
@@ -1378,7 +1383,6 @@ void VNA::SetupSCPI()
     scpi_freq->add(new SCPICommand("FULL", [=](QStringList params) -> QString {
         Q_UNUSED(params)
         SetFullSpan();
-        ResetLiveTraces();
         return SCPI::getResultName(SCPI::Result::Empty);
     }, nullptr));
     scpi_freq->add(new SCPICommand("ZERO", [=](QStringList params) -> QString {
@@ -1449,7 +1453,7 @@ void VNA::SetupSCPI()
         return QString::number(average.getLevel());
     }));
     scpi_acq->add(new SCPICommand("FINished", nullptr, [=](QStringList) -> QString {
-        return average.getLevel() == averages ? SCPI::getResultName(SCPI::Result::True) : SCPI::getResultName(SCPI::Result::False);
+        return average.settled() ? SCPI::getResultName(SCPI::Result::True) : SCPI::getResultName(SCPI::Result::False);
     }));
     scpi_acq->add(new SCPICommand("LIMit", nullptr, [=](QStringList) -> QString {
         return tiles->allLimitsPassing() ? "PASS" : "FAIL";
@@ -1855,6 +1859,7 @@ void VNA::ResetLiveTraces()
     traceModel.clearLiveData();
     UpdateAverageCount();
     UpdateCalWidget();
+    setOperationPending(true);
 }
 
 bool VNA::LoadCalibration(QString filename)
diff --git a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
index 79301a6..327147c 100644
--- a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
@@ -490,9 +490,6 @@ void AppWindow::SetupSCPI()
         SetInitialState();
         return SCPI::getResultName(SCPI::Result::Empty);
     }, nullptr));
-    scpi.add(new SCPICommand("*OPC", nullptr, [=](QStringList){
-        return "1";
-    }));
     auto scpi_dev = new SCPINode("DEVice");
     scpi.add(scpi_dev);
     scpi_dev->add(new SCPICommand("DISConnect", [=](QStringList params) -> QString {
diff --git a/Software/PC_Application/LibreVNA-GUI/averaging.cpp b/Software/PC_Application/LibreVNA-GUI/averaging.cpp
index 341f72c..79cae68 100644
--- a/Software/PC_Application/LibreVNA-GUI/averaging.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/averaging.cpp
@@ -84,6 +84,11 @@ unsigned int Averaging::currentSweep()
     }
 }
 
+bool Averaging::settled()
+{
+    return getLevel() == averages;
+}
+
 Averaging::Mode Averaging::getMode() const
 {
     return mode;
diff --git a/Software/PC_Application/LibreVNA-GUI/averaging.h b/Software/PC_Application/LibreVNA-GUI/averaging.h
index ab2ad4c..e77d4cf 100644
--- a/Software/PC_Application/LibreVNA-GUI/averaging.h
+++ b/Software/PC_Application/LibreVNA-GUI/averaging.h
@@ -26,6 +26,8 @@ public:
     // Returns the number of the currently active sweep. Value is incremented whenever the the first point of the sweep is added
     // Returned values are in range 0 (when no data has been added yet) to averages
     unsigned int currentSweep();
+    // Returns true if all required averages have been taken
+    bool settled();
     Mode getMode() const;
     void setMode(const Mode &value);
 
diff --git a/Software/PC_Application/LibreVNA-GUI/scpi.cpp b/Software/PC_Application/LibreVNA-GUI/scpi.cpp
index 6b5a89b..15a7e89 100644
--- a/Software/PC_Application/LibreVNA-GUI/scpi.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/scpi.cpp
@@ -5,6 +5,40 @@
 SCPI::SCPI() :
     SCPINode("")
 {
+    WAIexecuting = false;
+    OPCQueryScheduled = false;
+    OCAS = false;
+    ESR = 0x00;
+
+    add(new SCPICommand("*OPC", [=](QStringList){
+        // OPC command
+        if(isOperationPending()) {
+            OCAS = true;
+        }
+        return SCPI::getResultName(SCPI::Result::Empty);
+    }, [=](QStringList) -> QString {
+        // OPC query
+        if(isOperationPending()) {
+            // operation pending
+            OPCQueryScheduled = true;
+            OCAS = true;
+            return SCPI::getResultName(SCPI::Result::Empty);
+        } else {
+            // no operation, can return immediately
+            OCAS = false;
+            setFlag(Flag::OPC);
+            return "1";
+        }
+    }));
+
+    add(new SCPICommand("*WAI", [=](QStringList){
+        // WAI command
+        if(isOperationPending()) {
+            WAIexecuting = true;
+        }
+        return SCPI::getResultName(SCPI::Result::Empty);
+    }, nullptr));
+
     add(new SCPICommand("*LST", nullptr, [=](QStringList){
         QString list;
         createCommandList("", list);
@@ -95,23 +129,68 @@ QString SCPI::getResultName(SCPI::Result r)
 
 void SCPI::input(QString line)
 {
-    auto cmds = line.split(";");
-    SCPINode *lastNode = this;
-    for(auto cmd : cmds) {
-        if(cmd.size() > 0) {
-            if(cmd[0] == ':' || cmd[0] == '*') {
-                // reset to root node
-                lastNode = this;
+    cmdQueue.append(line);
+    process();
+}
+
+void SCPI::process()
+{
+    while(!WAIexecuting && !cmdQueue.isEmpty()) {
+        auto cmd = cmdQueue.front();
+        cmdQueue.pop_front();
+        auto cmds = cmd.split(";");
+        SCPINode *lastNode = this;
+        for(auto cmd : cmds) {
+            if(cmd.size() > 0) {
+                if(cmd[0] == ':' || cmd[0] == '*') {
+                    // reset to root node
+                    lastNode = this;
+                }
+                if(cmd[0] == ':') {
+                    cmd.remove(0, 1);
+                }
+                auto response = lastNode->parse(cmd, lastNode);
+                emit output(response);
             }
-            if(cmd[0] == ':') {
-                cmd.remove(0, 1);
-            }
-            auto response = lastNode->parse(cmd, lastNode);
-            emit output(response);
         }
     }
 }
 
+void SCPI::someOperationCompleted()
+{
+    if(!isOperationPending()) {
+        // all operations are complete
+        if(OCAS) {
+            OCAS = false;
+            setFlag(Flag::OPC);
+            if(OPCQueryScheduled) {
+                output("1");
+                OPCQueryScheduled = false;
+            }
+        }
+        if(WAIexecuting) {
+            WAIexecuting = false;
+            // process any queued commands
+            process();
+        }
+    }
+}
+
+void SCPI::setFlag(Flag flag)
+{
+    ESR |= ((int) flag);
+}
+
+void SCPI::clearFlag(Flag flag)
+{
+    ESR &= ~((int) flag);
+}
+
+bool SCPI::getFlag(Flag flag)
+{
+    return ESR & (int) flag;
+}
+
 SCPINode::~SCPINode()
 {
     if(parent) {
@@ -235,6 +314,36 @@ bool SCPINode::changeName(QString newname)
     return true;
 }
 
+void SCPINode::setOperationPending(bool pending)
+{
+    if(operationPending != pending) {
+        operationPending = pending;
+        if(!operationPending) {
+            // operation completed, needs to perform check if all operations are complete
+            auto root = this;
+            while(root->parent) {
+                root = root->parent;
+            }
+            auto scpi = static_cast<SCPI*>(root);
+            scpi->someOperationCompleted();
+        }
+    }
+}
+
+bool SCPINode::isOperationPending()
+{
+    if(operationPending) {
+        return true;
+    }
+    for(auto node : subnodes) {
+        if(node->isOperationPending()) {
+            return true;
+        }
+    }
+    // no node has any pending operations
+    return false;
+}
+
 bool SCPINode::nameCollision(QString name)
 {
     for(auto n : subnodes) {
diff --git a/Software/PC_Application/LibreVNA-GUI/scpi.h b/Software/PC_Application/LibreVNA-GUI/scpi.h
index 10634cf..5c5bb62 100644
--- a/Software/PC_Application/LibreVNA-GUI/scpi.h
+++ b/Software/PC_Application/LibreVNA-GUI/scpi.h
@@ -31,7 +31,7 @@ class SCPINode {
     friend class SCPI;
 public:
     SCPINode(QString name) :
-        name(name), parent(nullptr){}
+        name(name), parent(nullptr), operationPending(false){}
     virtual ~SCPINode();
 
     bool add(SCPINode *node);
@@ -44,6 +44,11 @@ public:
 
     bool changeName(QString newname);
 
+protected:
+    void setOperationPending(bool pending);
+
+    bool isOperationPending();
+
 private:
     QString parse(QString cmd, SCPINode* &lastNode);
     bool nameCollision(QString name);
@@ -52,6 +57,7 @@ private:
     std::vector<SCPINode*> subnodes;
     std::vector<SCPICommand*> commands;
     SCPINode *parent;
+    bool operationPending;
 };
 
 class SCPI : public QObject, public SCPINode
@@ -77,10 +83,39 @@ public:
 
     static QString getResultName(SCPI::Result r);
 
+    // call whenever a subnode completes an operation
+    void someOperationCompleted();
+
 public slots:
     void input(QString line);
+    void process();
 signals:
     void output(QString line);
+
+private:
+
+    enum class Flag  {
+        OPC = 0x01, // Operation complete
+        RQC = 0x02, // device wants to become the controller (of the bus)
+        QYE = 0x04, // query error
+        DDE = 0x08, // device-dependent error
+        EXE = 0x10, // execution error
+        CME = 0x20, // command error
+        URQ = 0x40, // user request
+        PON = 0x80, // power on
+    };
+
+    void setFlag(Flag flag);
+    void clearFlag(Flag flag);
+    bool getFlag(Flag flag);
+
+    unsigned int ESR;
+
+    bool OCAS;
+    bool OPCQueryScheduled;
+    bool WAIexecuting;
+
+    QList<QString> cmdQueue;
 };
 
 #endif // SCPI_H