# Exercise 4: Plotting a derived variable
**(10 minutes)**

Make a histogram of the new n-tuple variable **`pt`**. Don't forget to
include error bars and to label the axes; remember that the momenta
are in _GeV_.

:::{hint}
Are you getting a message about **`pt`** not being defined?
Remember that **`pt`** was defined for our "new" n-tuple
`definept`, not the original `dataframe`.
:::

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

<img src="https://imgs.xkcd.com/comics/newton_and_leibniz.png" alt="xkcd newton_and_leibniz" width="75%">

<https://xkcd.com/626/> by Randall Munroe
:::