And this also shows you can see from algebra and basic calculus that ends, this becomes zero or tenths of zero. That is, as TC decreases and Th increases or the difference between these two guys increases, the efficiency also increases. Okay? You can pluck some values in and you'll see that as this becomes smaller and this becomes larger, that E becomes more efficient. Okay, finally, let's talk about refrigerators and air conditioners. So refrigerators and air conditioners are basically reverse heat engines.