 So what do we do if we want to add two measurements with uncertainties? For example, I had a measurement of five centimeters plus minus one, like a stick of this length could have been here, could have been here. And I want to add another measurement of six centimeters plus minus two, so another stick that could have been shorter or could have been longer. If you think you're adding the sticks one to another, it's clear that the uncertainties they add up. Because now, instead of only uncertainties like this, you could be worst case be uncertain of this plus the other uncertainties. So what do we do? We add the absolute uncertainties. So what does this mean in this case? I'm taking my five centimeters, I add the six centimeters, I get eleven. So I take the best case scenario and then I take the one centimeters plus the two centimeters, gives me three centimeters. And that's it. So simply add the absolute uncertainties. If you're multiplying or divide values with uncertainties, we use another rule. Remember when we added and subtracted ten, we added the absolute uncertainties. For multiplying, this won't work. Thinking, for example, if I have a long room of a length of 100 meters plus minus 10 meters and the width of 10 meters plus minus two. And I want to figure out, okay, what's the surface area of this room? I will have to multiply these two values. So in this case, what we do is we add the relative uncertainties. So this is actually why we have relative uncertainties. So first step, if you do this, you have to transform your absolute uncertainties in relative ones. So 10 meters plus minus two divided by 10 times 100 percent gives me 20 percent. And 100 plus minus 10 meters gives me 100 meter plus minus 10 percent. Now, what I do for the value itself is simply multiply by 10 meters with the 100 meters. So I have 10 meters times 100 meters. And then how much could that be off? I'm adding the percentage values. So 20 percent plus 10 percent. So what I get is 100 is 1000 square meter plus minus a total uncertainty of 30 percent. Now, if I wanted to convert this back into absolute, I can. So this means 1000 square meters, 30 percent of 1000 is 300. So I could give this as the final answer. So if you have to multiply or divide certain things with uncertainties at the relative uncertainties, if you want to add and subtract, you add the absolute uncertainty.