To work with a system to control machines, users usually need to use HMI or industrial computer. In science fiction, HMI is sometimes used to refer to what is better described as direct neural interface. However, this latter usage is seeing increasing application in the real-life use of (medical) prostheses??the artificial extension that replaces a missing body part (e.g., cochlear implants). 8.4" HMI IPCdevice IEC-608NF /product/8.4_inch_HMI_touch_panel_pc_IEC-608NF/ In some circumstance computers might observe the user, and react according to their actions without specific commands. A means of tracking parts of the body is required, and sensors noting the position of the head, direction of gaze and so on have been used experimentally. This is particularly relevant to immersive interfaces. The goal of HMI (human-machine interface) engineering is to produce a user interface which makes it easy, efficient, and enjoyable to operate a machine in the way which produces the desired result. This generally means that the operator needs to provide minimal input to achieve the desired output, and also that the machine minimizes undesired outputs to the human.