diff --git a/.gitignore b/.gitignore
index 2bd99ec81..9c636d134 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@ jnq*
 *.mod
 *.pro.user
 *.txt
+!**/CMakeLists.txt
 cmake-build-debug
 cmake-build-release
 CMakeFiles
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f160d6b82..17f863042 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -926,7 +926,9 @@ endif ()
 if (WSJT_GENERATE_DOCS)
   add_subdirectory (doc)
 endif (WSJT_GENERATE_DOCS)
-
+if (EXISTS ${CMAKE_SOURCE_DIR}/tests AND IS_DIRECTORY ${CMAKE_SOURCE_DIR}/tests)
+  add_subdirectory (tests)
+endif ()
 
 #
 # Library building setup
diff --git a/qt_helpers.cpp b/qt_helpers.cpp
index 3f41d0f87..dd474e191 100644
--- a/qt_helpers.cpp
+++ b/qt_helpers.cpp
@@ -37,14 +37,14 @@ void update_dynamic_property (QWidget * widget, char const * property, QVariant
   widget->update ();
 }
 
-QDateTime qt_round_date_time_to (QDateTime dt, int seconds)
+QDateTime qt_round_date_time_to (QDateTime dt, int milliseconds)
 {
-  dt.setSecsSinceEpoch (dt.addSecs (seconds - 1).toSecsSinceEpoch () / seconds * seconds);
+  dt.setMSecsSinceEpoch (dt.addMSecs (milliseconds / 2).toMSecsSinceEpoch () / milliseconds * milliseconds);
   return dt;
 }
 
-QDateTime qt_truncate_date_time_to (QDateTime dt, int seconds)
+QDateTime qt_truncate_date_time_to (QDateTime dt, int milliseconds)
 {
-  dt.setSecsSinceEpoch (dt.toSecsSinceEpoch () / seconds * seconds);
+  dt.setMSecsSinceEpoch (dt.toMSecsSinceEpoch () / milliseconds * milliseconds);
   return dt;
 }
diff --git a/qt_helpers.hpp b/qt_helpers.hpp
index 638c50e2a..aae8c5f07 100644
--- a/qt_helpers.hpp
+++ b/qt_helpers.hpp
@@ -69,11 +69,11 @@ QString font_as_stylesheet (QFont const&);
 // conditional style sheet updates
 void update_dynamic_property (QWidget *, char const * property, QVariant const& value);
 
-// round a QDateTime instance to an interval
-QDateTime qt_round_date_time_to (QDateTime dt, int seconds);
+// round a QDateTime instance to an integral interval of milliseconds
+QDateTime qt_round_date_time_to (QDateTime dt, int milliseconds);
 
-// truncate a QDateTime to an interval
-QDateTime qt_truncate_date_time_to (QDateTime dt, int seconds);
+// truncate a QDateTime to an integral interval of milliseconds
+QDateTime qt_truncate_date_time_to (QDateTime dt, int milliseconds);
 
 template <class T>
 class VPtr
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
new file mode 100644
index 000000000..4b3462337
--- /dev/null
+++ b/tests/CMakeLists.txt
@@ -0,0 +1,23 @@
+find_package (Qt5Test 5 REQUIRED)
+
+#
+# Compiler options
+#
+set (CMAKE_CXX_STANDARD 11)
+add_compile_options ("$<$<COMPILE_LANGUAGE:Fortran>:-Wall;-Wno-conversion;-fno-second-underscore;-fno-f2c>")
+add_compile_options ("$<$<AND:$<COMPILE_LANGUAGE:Fortran>,$<CONFIG:Debug>>:-fbounds-check>")
+add_compile_options ("$<$<AND:$<COMPILE_LANGUAGE:Fortran>,$<NOT:$<CONFIG:Debug>>>:-funroll-all-loops>")
+add_compile_options ("$<$<AND:$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>,$<OR:$<C_COMPILER_ID:GNU>,$<C_COMPILER_ID:Clang>,$<C_COMPILER_ID:AppleClang>>>:-Wall;-Wextra>")
+add_compile_options ("$<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:GNU>>:-Wno-pragmas>")
+add_compile_options ("$<$<AND:$<OR:$<C_COMPILER_ID:GNU>,$<CXX_COMPILER_ID:GNU>>,$<NOT:$<CONFIG:Debug>>>:-fdata-sections;-ffunction-sections>")
+if (${OPENMP_FOUND} OR APPLE)
+  add_compile_options ("$<$<AND:$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>,$<C_COMPILER_ID:GNU>>:${OpenMP_C_FLAGS}>")
+endif ()
+
+# Tell CMake to run moc when necessary
+set (CMAKE_AUTOMOC ON)
+include_directories (${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_SOURCE_DIR})
+
+add_executable (test_qt_helpers test_qt_helpers.cpp)
+target_link_libraries (test_qt_helpers wsjt_qt Qt5::Test)
+add_test (test_qt_helpers test_qt_helpers)
diff --git a/tests/test_qt_helpers.cpp b/tests/test_qt_helpers.cpp
new file mode 100644
index 000000000..cb6744df2
--- /dev/null
+++ b/tests/test_qt_helpers.cpp
@@ -0,0 +1,138 @@
+#include <QtTest>
+#include <QDateTime>
+#include <QDebug>
+
+#include "qt_helpers.hpp"
+
+class TestQtHelpers
+  : public QObject
+{
+  Q_OBJECT
+
+public:
+
+private:
+  Q_SLOT void round_15s_date_time_up ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 500}};
+    QCOMPARE (qt_round_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 30)));
+  }
+
+  Q_SLOT void truncate_15s_date_time_up ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 500}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void round_15s_date_time_down ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 499}};
+    QCOMPARE (qt_round_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void truncate_15s_date_time_down ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 499}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void round_15s_date_time_on ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 15}};
+    QCOMPARE (qt_round_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void truncate_15s_date_time_on ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 15}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void round_15s_date_time_under ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 14, 999}};
+    QCOMPARE (qt_round_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void truncate_15s_date_time_under ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 14, 999}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15)));
+  }
+
+  Q_SLOT void round_15s_date_time_over ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 15, 1}};
+    QCOMPARE (qt_round_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void truncate_15s_date_time_over ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 15, 1}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 15000), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void round_7p5s_date_time_up ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 26, 250}};
+    QCOMPARE (qt_round_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 30)));
+  }
+
+  Q_SLOT void truncate_7p5s_date_time_up ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 26, 250}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void round_7p5s_date_time_down ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 26, 249}};
+    QCOMPARE (qt_round_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void truncate_7p5s_date_time_down ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 26, 249}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void round_7p5s_date_time_on ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 500}};
+    QCOMPARE (qt_round_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void truncate_7p5s_date_time_on ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 500}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void round_7p5s_date_time_under ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 499}};
+    QCOMPARE (qt_round_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void truncate_7p5s_date_time_under ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 499}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 15)));
+  }
+
+  Q_SLOT void round_7p5s_date_time_over ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 501}};
+    QCOMPARE (qt_round_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+
+  Q_SLOT void truncate_7p5s_date_time_over ()
+  {
+    QDateTime dt {QDate {2020, 8, 6}, QTime {14, 15, 22, 501}};
+    QCOMPARE (qt_truncate_date_time_to (dt, 7500), QDateTime (QDate (2020, 8, 6), QTime (14, 15, 22, 500)));
+  }
+};
+
+QTEST_MAIN (TestQtHelpers);
+
+#include "test_qt_helpers.moc"
diff --git a/widgets/mainwindow.cpp b/widgets/mainwindow.cpp
index 6c2a32c25..b91207089 100644
--- a/widgets/mainwindow.cpp
+++ b/widgets/mainwindow.cpp
@@ -8017,8 +8017,8 @@ void MainWindow::p1ReadFromStdout()                        //p1readFromStdout
 
 QString MainWindow::beacon_start_time (int n)
 {
-  auto bt = qt_truncate_date_time_to (QDateTime::currentDateTimeUtc ().addSecs (n), m_TRperiod);
-  if (m_TRperiod < 60)
+  auto bt = qt_truncate_date_time_to (QDateTime::currentDateTimeUtc ().addSecs (n), m_TRperiod * 1.e3);
+  if (m_TRperiod < 60.)
     {
       return bt.toString ("HHmmss");
     }