diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/caldevice.cpp b/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/caldevice.cpp
index 92f3814..7bc1ada 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/caldevice.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/caldevice.cpp
@@ -1,7 +1,10 @@
 #include "caldevice.h"
 
+#include "Util/util.h"
+
 #include <QDebug>
 #include <QDateTime>
+
 using namespace std;
 
 static QString getLocalDateTimeWithUtcOffset()
@@ -173,7 +176,7 @@ void CalDevice::loadCoefficientSets(QStringList names, bool fast)
 {
     coeffSets.clear();
     abortLoading = false;
-    if(fast) {
+    if(fast && Util::firmwareEqualOrHigher(firmware, "0.2.1")) {
         loadThread = new std::thread(&CalDevice::loadCoefficientSetsThreadFast, this, names);
     } else {
         loadThread = new std::thread(&CalDevice::loadCoefficientSetsThreadSlow, this, names);
diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/usbdevice.cpp b/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/usbdevice.cpp
index a6d89e7..7915efd 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/usbdevice.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/LibreCAL/usbdevice.cpp
@@ -212,7 +212,6 @@ void USBDevice::SearchDevices(std::function<bool (libusb_device_handle *, QStrin
 
 bool USBDevice::send(const QString &s)
 {
-//    qDebug() << "Send:"<<s;
     unsigned char data[s.size()+2];
     memcpy(data, s.toLatin1().data(), s.size());
     memcpy(&data[s.size()], "\r\n", 2);
@@ -244,7 +243,6 @@ bool USBDevice::receive(QString *s, unsigned int timeout)
 void USBDevice::ReceivedData()
 {
     uint16_t handled_len;
-//    qDebug() << "received new data";
     unique_lock<mutex> lck(mtx);
     do {
         handled_len = 0;
@@ -255,7 +253,6 @@ void USBDevice::ReceivedData()
 
             // add received line to buffer
             lineBuffer.append(line);
-//            qDebug() << "append" << line << "size" << lineBuffer.size();
 
             usbBuffer->removeBytes(handled_len + 1);
         }
@@ -263,7 +260,6 @@ void USBDevice::ReceivedData()
     if(lineBuffer.size() > 0) {
         cv.notify_one();
     }
-//    qDebug() << "notify done";
 }
 
 void USBDevice::flushReceived()
diff --git a/Software/PC_Application/LibreVNA-GUI/Util/util.cpp b/Software/PC_Application/LibreVNA-GUI/Util/util.cpp
index 5bd8284..8dce2ea 100644
--- a/Software/PC_Application/LibreVNA-GUI/Util/util.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Util/util.cpp
@@ -201,3 +201,27 @@ QColor Util::getIntensityGradeColor(double intensity)
         return Qt::black;
     }
 }
+
+bool Util::firmwareEqualOrHigher(QString firmware, QString compare)
+{
+    QStringList f = firmware.split(".");
+    QStringList c = compare.split(".");
+    if(f.size() != 3 || c.size() != 3) {
+        return false;
+    }
+    if(f[0].toInt() < c[0].toInt()) {
+        return false;
+    } else if(f[0].toInt() > c[0].toInt()) {
+        return true;
+    }
+    if(f[1].toInt() < c[1].toInt()) {
+        return false;
+    } else if(f[1].toInt() > c[1].toInt()) {
+        return true;
+    }
+    if(f[2].toInt() < c[2].toInt()) {
+        return false;
+    } else {
+        return true;
+    }
+}
diff --git a/Software/PC_Application/LibreVNA-GUI/Util/util.h b/Software/PC_Application/LibreVNA-GUI/Util/util.h
index 4963a52..47c6bb7 100644
--- a/Software/PC_Application/LibreVNA-GUI/Util/util.h
+++ b/Software/PC_Application/LibreVNA-GUI/Util/util.h
@@ -166,6 +166,8 @@ namespace Util {
 
     // intensity color scale, input value from 0.0 to 1.0
     QColor getIntensityGradeColor(double intensity);
+
+    bool firmwareEqualOrHigher(QString firmware, QString compare);
 }
 
 #endif // UTILH_H
diff --git a/Software/PC_Application/LibreVNA-Test/utiltests.cpp b/Software/PC_Application/LibreVNA-Test/utiltests.cpp
index 95d3f4e..c8badd3 100644
--- a/Software/PC_Application/LibreVNA-Test/utiltests.cpp
+++ b/Software/PC_Application/LibreVNA-Test/utiltests.cpp
@@ -63,3 +63,18 @@ void UtilTests::NoisyCircleApproximation()
     QVERIFY(abs(center.real() - circCenter.real()) <= maxDelta);
     QVERIFY(abs(center.imag() - circCenter.imag()) <= maxDelta);
 }
+
+void UtilTests::FirmwareComparison()
+{
+    QVERIFY(Util::firmwareEqualOrHigher("3.1.2", "2.1.2") == true);
+    QVERIFY(Util::firmwareEqualOrHigher("2.1.2", "2.0.2") == true);
+    QVERIFY(Util::firmwareEqualOrHigher("2.1.2", "2.1.1") == true);
+    QVERIFY(Util::firmwareEqualOrHigher("2.1.2", "2.1.2") == true);
+    QVERIFY(Util::firmwareEqualOrHigher("2.1.1", "2.1.2") == false);
+
+    QVERIFY(Util::firmwareEqualOrHigher("2.2.2", "2.3.1") == false);
+    QVERIFY(Util::firmwareEqualOrHigher("2.2.2", "2.1.3") == true);
+
+    QVERIFY(Util::firmwareEqualOrHigher("2.2.2", "2.3") == false);
+    QVERIFY(Util::firmwareEqualOrHigher("2.2", "2.3.1") == false);
+}
diff --git a/Software/PC_Application/LibreVNA-Test/utiltests.h b/Software/PC_Application/LibreVNA-Test/utiltests.h
index 2c19026..4ac676a 100644
--- a/Software/PC_Application/LibreVNA-Test/utiltests.h
+++ b/Software/PC_Application/LibreVNA-Test/utiltests.h
@@ -13,6 +13,7 @@ private slots:
     void IdealCircleApproximation();
     void IdealArcApproximation();
     void NoisyCircleApproximation();
+    void FirmwareComparison();
 };
 
 #endif // UTILTESTS_H