How to choose the Gaussian noise of a Sensor?

I am using **Velodyne VLP16** Lidar at my simulations. I found the plugin below from [here](https://github.com/tu-darmstadt-ros-pkg/hector_models/blob/kinetic-devel/hector_sensors_description/urdf/vlp16.urdf.xacro);>${ros_topic}${name}_frame0.45130.00.008 And I wonder why Gaussian Noise is set to **0.008** and how can it be measured? This is the sensor specifications;