# Exercise 2: Add error bars to a histogram 
**(5 minutes)**

We're still plotting the **`chi2`** histogram as a solid curve. Most of
the time, your supervisor will want to see histograms with errors.
Revise the `Analyze::Terminate` method in Analyze.C to draw the
histograms with error bars.

:::::{admonition} Hint
:class: tip
Look back at {ref}`Working with Histograms <working-with-histograms>`.

:::{warning}
The histogram may not be immediately visible, because all the
points are squeezed into the left-hand side of the plot. We'll
investigate the reason why in a subsequent exercise.

After you make a change to Analyze.C, you have to restart ROOT before
you run
`tree1->Process("Analyze.C")` again. Don't forget the up-arrow key!
:::
:::::

:::{figure-md} chi2-errors-c-fig
:class: align-center

<img src="../chi2-histogram.png" alt="chi2 histogram">

What I get when I plot chi2 with errors bars turned on.
:::

:::{note}
See {ref}`this note in the Python tutorial <making-a-plot>` for how I made this plot.
:::