Calculating Fungicide for Apples

I have trouble calculating the amount of spray I need for my apples. Can I save what's left over for the next application?

Melinda:

Once mixed, fungicide needs to be used as soon as possible. Leftover mixtures won't provide adequate control. Keep records of what you use and what's left over to help you mix the right amount the next time. If you still have too much, maybe your neighbors would appreciate your help in controlling diseases on their apples.