diff --git a/gui.cpp b/gui.cpp
index 029d9b5..dda4818 100644
--- a/gui.cpp
+++ b/gui.cpp
@@ -4,6 +4,7 @@
 
 
 wxMenu *port_menu;
+wxMenu *sendcal_menu;
 wxString port_name;
 
 
@@ -60,6 +61,7 @@ void MyCanvas::InitGL()
 BEGIN_EVENT_TABLE(MyFrame,wxFrame)
 	EVT_MENU(wxID_ABOUT, MyFrame::OnAbout)
 	EVT_MENU(wxID_EXIT, MyFrame::OnQuit)
+	EVT_MENU(ID_SENDCAL, MyFrame::OnSendCal)
 	EVT_TIMER(ID_TIMER, MyFrame::OnTimer)
 	EVT_MENU_RANGE(9000, 9999, MyFrame::OnPort)
 	EVT_MENU_OPEN(MyMenu::OnShowPortList)
@@ -77,6 +79,9 @@ MyFrame::MyFrame(wxWindow *parent, wxWindowID id, const wxString &title,
 
 	menuBar = new wxMenuBar;
 	menu = new wxMenu;
+	menu->Append(ID_SENDCAL, wxT("Send Calibration"));
+	sendcal_menu = menu;
+	sendcal_menu->Enable(ID_SENDCAL, false);
 	menu->Append(wxID_EXIT, wxT("Quit"));
 	menuBar->Append(menu, wxT("&File"));
 
@@ -123,10 +128,31 @@ MyFrame::MyFrame(wxWindow *parent, wxWindowID id, const wxString &title,
 void MyFrame::OnTimer(wxTimerEvent &event)
 {
 	//printf("OnTimer\n");
-	read_serial_data();
-	m_canvas->Refresh();
+	if (port_is_open()) {
+		read_serial_data();
+		m_canvas->Refresh();
+		if (magcal.FitError < 6.0f) {
+			sendcal_menu->Enable(ID_SENDCAL, true);
+		} else if (magcal.FitError > 7.0f) {
+			sendcal_menu->Enable(ID_SENDCAL, false);
+		}
+	} else {
+		sendcal_menu->Enable(ID_SENDCAL, false);
+	}
 }
 
+void MyFrame::OnSendCal(wxCommandEvent &event)
+{
+	printf("OnSendCal\n");
+	printf("Magnetic Calibration:   (%.1f%% fit error)\n", magcal.FitError);
+	printf("   %7.2f   %6.3f %6.3f %6.3f\n",
+		magcal.V[0], magcal.invW[0][0], magcal.invW[0][1], magcal.invW[0][2]);
+	printf("   %7.2f   %6.3f %6.3f %6.3f\n",
+		magcal.V[1], magcal.invW[1][0], magcal.invW[1][1], magcal.invW[1][2]);
+	printf("   %7.2f   %6.3f %6.3f %6.3f\n",
+		magcal.V[2], magcal.invW[2][0], magcal.invW[2][1], magcal.invW[2][2]);
+	send_calibration();
+}
 
 void MyFrame::OnPort(wxCommandEvent &event)
 {
@@ -135,6 +161,7 @@ void MyFrame::OnPort(wxCommandEvent &event)
 
 	close_port();
         //printf("OnPort, id = %d, name = %s\n", id, (const char *)name);
+	sendcal_menu->Enable(ID_SENDCAL, false);
 	port_name = name;
         if (id == 9000) return;
 	raw_data_reset();
@@ -186,10 +213,11 @@ void MyMenu::OnShowPortList(wxMenuEvent &event)
         menu->AppendRadioItem(9000, " (none)");
         wxArrayString list = serial_port_list();
         num = list.GetCount();
+	bool isopen = port_is_open();
         for (int i=0; i < num; i++) {
                 //printf("%d: port %s\n", i, (const char *)list[i]);
                 menu->AppendRadioItem(9001 + i, list[i]);
-                if (port_name.IsSameAs(list[i])) {
+                if (isopen && port_name.IsSameAs(list[i])) {
                         menu->Check(9001 + i, true);
                         any = 1;
                 }
diff --git a/gui.h b/gui.h
index 14c25f9..7dfc807 100644
--- a/gui.h
+++ b/gui.h
@@ -24,6 +24,7 @@
 
 
 #define ID_TIMER		10000
+#define ID_SENDCAL		10001
 
 
 class MyCanvas : public wxGLCanvas
@@ -62,6 +63,7 @@ public:
 	~MyFrame(void);
 	void InitGL();
 	void OnPort(wxCommandEvent &event);
+	void OnSendCal(wxCommandEvent &event);
 private:
 	MyCanvas *m_canvas;
 	wxTimer *m_timer;
diff --git a/imuread.h b/imuread.h
index 946ed08..ac33d69 100644
--- a/imuread.h
+++ b/imuread.h
@@ -60,6 +60,7 @@ typedef struct {
 } Quaternion_t;
 extern Quaternion_t current_orientation;
 
+extern int port_is_open(void);
 extern int open_port(const char *name);
 extern int read_serial_data(void);
 extern int write_serial_data(const void *ptr, int len);
diff --git a/serialdata.c b/serialdata.c
index 7a48a09..5885403 100644
--- a/serialdata.c
+++ b/serialdata.c
@@ -245,6 +245,12 @@ static void newdata(const unsigned char *data, int len)
 
 static int portfd=-1;
 
+int port_is_open(void)
+{
+	if (portfd > 0) return 1;
+	return 0;
+}
+
 int open_port(const char *name)
 {
 	struct termios termsettings;
@@ -279,7 +285,7 @@ int read_serial_data(void)
 		if (n > 0 && n <= sizeof(buf)) {
 			newdata(buf, n);
 			nodata_count = 0;
-			//return n;
+			return n;
 		} else if (n == 0) {
 			if (++nodata_count > 6) {
 				close_port();
@@ -339,7 +345,13 @@ void close_port(void)
 
 #elif defined(WINDOWS)
 
-static HANDLE port_handle;
+static HANDLE port_handle=INVALID_HANDLE_VALUE;
+
+int port_is_open(void)
+{
+	if (port_handle == INVALID_HANDLE_VALUE) return 0;
+	return 1;
+}
 
 int open_port(const char *name)
 {