documentation for new calibration check code

stretch_calibration/README.md

@@ -8,6 +8,21 @@ Hello Robot Inc. uses this code to calibrate each robot prior to shipping. Users
 
 In addition, after changing a tool, this code can be used to generate a new calibrated URDF that incorporates the tool without performing a new calibration optimization. 
 
+## Checking the Current Calibration with New Observations
+
+1. Collect new observations
+
+   `roslaunch stretch_calibration collect_check_head_calibration_data.launch`
+   
+2. Test how well the current calibrated model fits the new observations
+
+   `rosrun stretch_calibration check_head_calibration.sh`
+   
+   - In RViz the white markers represent the locations for the ArUco markers predicted by the calibrated URDF. The colored markers represent the observed locations of the ArUco markers on the robot's body. For a good fit, the white markers will be close to the colored markers. 
+   
+   - The total_error printed on the command line should be less than 0.05. If it is not, an error will be printed on the command line. 
+
+
 ## Visually Inspecting the Current Calibration
 
 The following command will allow you to visually inspect a calibration with Rviz. You can use RViz to see how well the robot's 3D body model matches point clouds from the 3D camera. While visualizing the 3D model and point clouds in RViz, you can use keyboard commands in the terminal to move the head around, the lift up and down, and the arm in and out. The keyboard commands will be printed in the terminal.