# Exercise 5: Scatterplot 
**(10 minutes)**

Now add another plot: a scatterplot of **`chi2`** versus **`ebeam`**. Don't
forget to label the axes!

:::{hint}
Remember back in {ref}`Exercise 1 <detective-work>`, I asked you to figure out the name
`TF2` given that the name of the 1-dimensional function class was
`TF1`? Well, the name of the one-dimensional histogram class is
`TH1D`, so what do you think the name of the two-dimensional histogram
class is? Check your guess on the ROOT web site.

To fill a one-dimensional histogram, e.g., `chi2hist`, you use a
`Fill` command with a single argument:

    chi2hist.Fill(chi2);

How do you think you might fill a two-dimensional histogram? Check
your answer on the ROOT web site.
:::

:::{figure-md} linear_regression-fig
:class: align-center

<img src="https://imgs.xkcd.com/comics/linear_regression.png" alt="xkcd linear_regression" width="70%">

<https://xkcd.com/1725/> by Randall Munroe
:::