A farmer records the number of days x since a seedling was planted and its height y in centimetres…

Step 1. The six points. $S_{xx} = 17.5$, $S_{xy} = 27$ and $S_{yy} = 42$. So $r = \dfrac{27}{\sqrt{17.5 \times 42}} = 0.996$. The slope is $\dfrac{27}{17.5} = 1.543$.

Step 2. Add $(7, 6)$. For seven points, $\bar{x} = 4$ and $\bar{y} = 6.857$. Then $S_{xx} = 28$, $S_{xy} = 24$ and $S_{yy} = 42.857$, so $r = \dfrac{24}{\sqrt{28 \times 42.857}} = 0.693$.

Step 3. Add $(7, 2)$. Now $\bar{y} = 6.286$, $S_{xy} = 12$, $S_{yy} = 63.43$, so $r = \dfrac{12}{\sqrt{28 \times 63.43}} = 0.285$.

What it means. The line was a close fit for the first six days. The storm record is an outlier. It reflects an accident, not growth, so the seven-point $r$ does not describe a healthy plant. Report the storm separately.