For example, the product hopper is represented as a fuel tank, regardless of the specific device used to perform this function. Its status is displayed through the adoption of universal color codes: “green” when the container is full, “orange” when it is almost empty and, finally, “red” when all the product is finished. 

Users search for clues, for any sign that might help them cope and understand.  As they are drawn up, the icons of XIMA act as perceivable indicators that suggest appropriate functions to the operator.