 Hello, this is Professor Steven Esheba and I want to tell you a little bit about entering expressions in a spreadsheet. So an expression, unlike a number, begins with an equal sign, so I'm going to put that equal sign here. And the idea is that I want to, in this case, calculate a pressure of a gas times the volume of a gas that's in, say, an Erlenmeyer flask. And I've written down some of these numbers here. The pressure could be 1, so I could just say 1. Then to multiply, I say star or asterisk, and then the volume I can see is 0.25, and that's in liters, because we're working with, say, a 250 milliliter flask. And in that case, it's pretty not very complicated calculation. Now what I, what you often want to do, however, is instead of hardwiring, what's called hardwiring that number, I want to refer to that value there in that cell, and that value in that cell. So what I'm going to do is a little bit different here. I'm going to still say equals, but instead of saying equals 1, I'm going to click in that box. And you see that was box B14, so that's why the number B14 showed up. Now I'm going to put an asterisk, because I want to multiply that by the volume, which is in cell B15, and as you can see, I get the same answer. And that might seem like an unnecessary amount of work, but quite often you want to reuse the same numbers frequently, or maybe you would like to change this pressure and then have all of your other cells updated automatically, and that's really why we like to point to two different cells when we're doing a calculation like that.