diff --git a/printrun/printcore.py b/printrun/printcore.py
index 0845052a..52672be3 100644
--- a/printrun/printcore.py
+++ b/printrun/printcore.py
@@ -417,16 +417,15 @@ def startprint(self, gcode, startindex = 0):
 
         self.clear = False
         
-        '''Reset Gcode line number for printer
+        '''Reset Gcode line number for printer, pls. see issue #1421.
            Actual Prusa firmware >3.12.x needs "M110 N-1"
            Smoothieware firmware needs "N-1 M110"
            Old Marlin firmware 1.0.0 needs in addition line checksum
-           self._send("M110 N-1", -1, True) work for Smoothieware and old Marlin firmware.
-           Test for Prusa is needed
+           self._send("M110 N-1", -1, True) results in sending "N-1 M110 N-1*125" 
+           and do not harm Smoothieware and old Marlin firmware.
+           Test for Prusa is needed.
         '''
-        #self._send("M110 N-1") #Prusa firmware >3.12.x
         self._send("M110 N-1", -1, True) #all in one if Prusa works with "N-1 M110 N-1 + checksum"
-        #self._send("M110", -1, True) #older or other firmware, like Smoothieware + Marlin 1.0 needs checksum in addition
 
         resuming = (startindex != 0)
         self.print_thread = threading.Thread(target = self._print,
@@ -686,16 +685,15 @@ def _sendnext(self):
                 self.queueindex = 0
                 self.lineno = 0
 
-                '''Reset Gcode Line number for Printer
-                Actual Prusa firmware >3.12.x needs "M110 N-1"
-                Smoothieware firmware needs "N-1 M110"
-                Old Marlin firmware 1.0.0 needs in addition line checksum
-                self._send("M110 N-1", -1, True) work for Smoothieware and old Marlin firmware.
-                Test for Prusa is needed
+                '''Reset Gcode line number for printer, pls. see issue #1421.
+                   Actual Prusa firmware >3.12.x needs "M110 N-1"
+                   Smoothieware firmware needs "N-1 M110"
+                   Old Marlin firmware 1.0.0 needs in addition line checksum
+                   self._send("M110 N-1", -1, True) results in sending "N-1 M110 N-1*125" 
+                   and do not harm Smoothieware and old Marlin firmware.
+                   Test for Prusa is needed.
                 '''
-                #self._send("M110 N-1") #Prusa firmware >3.12.x
                 self._send("M110 N-1", -1, True) #all in one if Prusa works with "N-1 M110 N-1 + checksum"
-                #self._send("M110", -1, True) #older or other firmware, like Smoothieware + Marlin 1.0 needs checksum in addition
 
     def _send(self, command, lineno = 0, calcchecksum = False):
         # Only add checksums if over serial (tcp does the flow control itself)
diff --git a/testfiles/arc_test.gcode b/testfiles/arc_test.gcode
new file mode 100644
index 00000000..46364e41
--- /dev/null
+++ b/testfiles/arc_test.gcode
@@ -0,0 +1,21 @@
+; Print this file for a quick test of support for arc movements with 
+; G2 and G3 and z helix movement up and down +- 10 mm, 6 times a full cycle
+; It takes only a half minute and prints above the print bed (z=20 mm)
+; w/o heating and extrusion
+
+G28 ; home
+G0 Z10.0000 S0 ; lift z
+G90 ; absolute mode
+G21	; set unit to mm
+
+G2 X15 Y20 I30 J40 Z20 F8000
+G3 X15 Y20 I30 J40 Z10 F8000
+G2 X15 Y20 I30 J40 Z20 F8000
+G3 X15 Y20 I30 J40 Z10 F8000
+G2 X15 Y20 I30 J40 Z20 F8000
+G3 X15 Y20 I30 J40 Z10 F8000
+
+G0 X5.0000
+G0 Y5.0000
+
+M84; motors off
\ No newline at end of file
diff --git a/testfiles/quicktest.gcode b/testfiles/quicktest.gcode
index ce50d9f4..643d83bf 100644
--- a/testfiles/quicktest.gcode
+++ b/testfiles/quicktest.gcode
@@ -1,7 +1,13 @@
-G28
-G0 Z10.0000 S0
-G90
-G21
+; Print this little gcode file for a quick test for repeated prints
+; Area needed from homing position: x78 y70 z10 mm
+; It takes only a half minute and prints above the print bed (z=7 mm)
+; w/o heating and extrusion
+
+G28 ; home
+G0 Z10.0000 S0 ; lift z
+G90 ; absolute mode
+G21	; set unit to mm
+
 G0 F2000
 G0 Z 7.0000
 G0 X 38.0000 Y 70.0000
@@ -34,5 +40,6 @@ G1 X 20.0000 Y 60.0000
 G0 Z10.0000
 G0 X5.0000
 G0 Y5.0000
-M84; motors off
+
+M84 ; motors off