diff --git a/README.md b/README.md
index e0b0e62..e2f6e9e 100644
--- a/README.md
+++ b/README.md
@@ -61,8 +61,9 @@ ros2 run robot_controller dummy_controller
 ```
 
 AxidrawController draws on the axidraw robot
+Find the serial device in "/dev/", it is usually named "/dev/ttyACMX" where X is usually 0.
 ``` sh
-ros2 launch axidraw_controller axidraw_controller
+ros2 launch axidraw_controller axidraw_controller serial_port:=/dev/ttyACM0
 ```
 
 This starts the simulated lite6