I have just purchased and Indesit FIM31K.A. (GB) oven but I am confused with how to use it, It states that when starting oven to turn to temp required and turn Grill to max , I can not understand why I need to use Grill as well can you please explain to me, Also how do I know when the right temp is reached if the light stays on ? can you please advise me on these issues. kind regards.