diff --git a/COMTool/plugins/graph.py b/COMTool/plugins/graph.py
index a943910..59ac2e9 100644
--- a/COMTool/plugins/graph.py
+++ b/COMTool/plugins/graph.py
@@ -71,7 +71,9 @@ class Plugin(Plugin_Base):
  * $[line name],[x],[y]<,checksum>\\n
  *   ''' + _('"$" means start of frame, end with "\\n" "," means separator') + ''',
  *   ''' + _('checksum is optional, checksum is sum of all bytes in frame except ",checksum".') + '''
+ *   ''' + _('[x] is optional') + '''
  *   ''' + _('e.g.') + '''
+ *     "$roll,2.0\\n"
  *     "$roll,1.0,2.0\\n"
  *     "$pitch,1.0,2.0\\r\\n"
  *     "$pitch,1.0,2.0,179\\n" (179 = sum(b"$pitch,1.0,2.0") % 256)
@@ -79,6 +81,7 @@ class Plugin(Plugin_Base):
 int plot_pack_ascii(uint8_t *buff, int buff_len, const char *name, float x, float y)
 {
     snprintf(buff, buff_len, "$%s,%f,%f", name, x, y);
+    //snprintf(buff, buff_len, "$%s,%f", name, y);
     // add checksum
     int sum = 0;
     for (int i = 0; i < strlen(buff); i++)
diff --git a/COMTool/plugins/graph_widgets.py b/COMTool/plugins/graph_widgets.py
index 0755bc7..6acb9e5 100644
--- a/COMTool/plugins/graph_widgets.py
+++ b/COMTool/plugins/graph_widgets.py
@@ -46,6 +46,7 @@ def __init__(self, parent=None, hintSignal=lambda type, title, msg: None, rmCall
         self.setLayout(self.layout)
         self.plotWin = pg.GraphicsLayoutWidget()
         self.plotWin.setMinimumHeight(200)
+        self.default_x = 0;
         pg.setConfigOptions(antialias=True)
         rmBtn = QPushButton(_("Remove"))
         clearBtn = QPushButton(_("Clear"))
@@ -215,9 +216,11 @@ def decodeDataAscii(self, data: bytes):
         '''
             @data bytes, protocol:
                          $[line name],[x],[y]<,checksum>\n
+                         or $[line name],[y]
                          "$" means start of frame, "," means separator,
                             checksum is optional, checksum is sum of all bytes in frame except ",checksum".
                          e.g.
+                            "$roll,2.0\n"
                             "$roll,1.0,2.0\n"
                             "$pitch,1.0,2.0\r\n"
                             "$pitch,1.0,2.0,179\n" , the 179 = sum(ord(c) for c in "$pitch,1.0,2.0") % 256
@@ -245,12 +248,17 @@ def decodeDataAscii(self, data: bytes):
         frame = self.rawData[1:idx] # pitch,1.0,2.0  pitch,1.0,2.0,179
         self.rawData = self.rawData[idx + 1:]
         items = frame.split(b",")
-        if len(items) != 3 and len(items) != 4:
+        if len(items) != 2 and len(items) != 3 and len(items) != 4:
             print("-- format error, frame item len(%s, should 3 or 4) error: %s" % (len(items), frame))
             return False, self.data
         try:
-            x = float(items[1])
-            y = float(items[2])
+            if len(items) == 2:
+                x = float(self.default_x)
+                y = float(items[1])
+                self.default_x += 1
+            else:
+                x = float(items[1])
+                y = float(items[2])
         except Exception:
             print("-- x or y format error, frame: %s" % frame)
             return False, self.data