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All right.
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So in the last lesson, we figured out how to create 3D text to display our distance on screen, and we
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also figured out how to position it so that it's showing just at the point where we place our endpoint.
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So in this lesson, we're going to have a look at fixing some of the logical flaws that are in our app.
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So currently, if you add a third dot, the distance doesn't actually change,
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and that's because of these two lines here.
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We created this array called dotNode that keeps track of the dots on the scene that the user has placed,
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and every single time there's a new tab, we add another one to this array.
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But we're only calculating the distance between the zeroth and the first element in that array.
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So no matter how many more dots you add to the scene, you're not going to get a different distance.
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So to fix this, we're going to add some checking methods.
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So inside touchesBegan, what we want to do is that if there are two or more nodes inside this dotNode
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array, then we're going to remove all the previous ones and clear the board.
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And in this case, we're assuming that when the user touches the scene for the third time that they want
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to clear the previous measurements and start afresh,
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right?
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So to do that, we're going to say if dotNodes.count >= 2, then in that case,
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we're going to loop through the array,
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so for dot in dotNodes, and we're going to remove each dot in the array from the parentNode, 
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so removeFromParentNode.
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So this basically takes that 3D node off the scene and we now have no dots in the scene.
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So if you tap once, you get one dot. If you tap twice, you get the second dot, as well as the measurement
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of the distance.
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But if you tap the scene a third time, then it removes the previous two dots and it shows you your brand
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new dot.
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And then, after all of this is done, after we've removed all the dots from the scene, then we're going
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to clear this dotNodes array,
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so dotNodes equals a fresh array of SCNNodes,
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and we're going to initialize it to an empty array.
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So let's go ahead and run and test.
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All right.
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So you might have noticed that our dot removing code worked as expected.
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And whenever we tried to put on a third dot, then our code removes all the previous ones and calculates
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a new value.
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Now, the problem, though, is that our text is being rendered at the same position as the previous text,
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and the previous text isn't being removed.
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So let's go ahead and remove the textNode every single time we call updateText.
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So to do that, we're going to have to store this textNode, not inside here, but at the top of the file.
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So instead of saying let textNode equal this, I'm going to say textNode, and I'm going to create it
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up here.
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So var textNode = SCNNode.
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And whenever we call updateText, so that's when we want to display our distance as a 3D text, the first
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thing I'm gonna do is I'm going to say textNode.removeFromParentNode, so that clears the previous
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text, and then we can generate a new one using our code with the latest distance.
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So let's give it a spin.
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And there you have it, your very own real ruler.
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So you'll be able to measure things in the real world using your brand-new app created using ARKit.
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I hope you enjoyed that tutorial.
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Be sure to leave any questions in the  Q & A area and also let me know if there's anything else that
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you really want us to cover.
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And if it's really popular, then we'll look into it.
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So that's all from me, Angela at the London App Brewery,  and I'll see you on the next lesson.