 Now there's no sort of formula to learn or rules to learn about how to estimate things, really it's just something you learn to do by practice. So I'm going to do a few examples to give you a sort of an idea and then you can have a go at some yourself. So let's start off by trying to figure out what fraction of an Apple's price comes from the truck that transports it to the supermarket. Alright, so the first thing to realize is that we're going to have to make some guesses. We can't just answer this question because I have no idea how much of an Apple's price comes from its transport by truck. So I have some idea how much an Apple costs. There's my Apple and it costs maybe 50 cents. And now to have some idea of what it costs to transport a truck from say the farmers markets in Sydney down to Canberra. So I've got a truck full of apples traveling to Canberra. Now I'm going to guess that it costs maybe $500 for the human to drive down and back. That's basically a day's work. Maybe that's a massive overestimate. I don't know. And I'm going to guess that the petrol cost is going to be about another $100 or so. So that's two tanks of petrol for a car. Maybe that's a bit low, but it'll be the right ballpark. It won't be $1,000. And the $500 is probably a bit high because I understand that drivers lead fairly frugal lives. Okay, so the real question now in order to try and figure out how much of this 50 cents here is being affected by the cost of transport is to figure out how many apples are going to be in that truck. And this is where our guests are pretty bad. If you ask me to guess how many apples would fit in a truck, I'm not sure I could get it right to a factor of 10. So I'm going to do a little bit of thinking now. And this is where we use all our practice in scaling.