My new oven has a temperature selection knob -- pretty standard -- and another where I can choose convection, or broil, or fast heat, etc. But there are also two different settings (ROAST and BAKE) that seem the same to me. Is there a difference when I choose one over the other? If I use 'roast' for meats, say, and 'bake' for cakes and cookies, then which should I choose for a frozen pizza? How do I choose?