# Walkthrough: Simple analysis using the Draw command, part 2 
**(10 minutes)**

Instead of just plotting a single variable, let's try plotting two
variables at once:

    tree1.Draw("ebeam:px")
    my_canvas.Draw()

:::{note}
This is a scatterplot, a handy way of observing the correlations between
two variables. The `Draw` command interprets the variables as
("y:x") to decide which axes to use.

It's easy to fall into the trap of thinking that each (x,y) point on a
scatterplot represents two values in your n-tuple. The scatterplot is a
grid; each square in the grid is randomly populated with a density of
dots proportional to the number of values in that square.
:::

Try making scatterplots of different pairs of variables. Do you see any
correlations?

:::{note}
If you see a shapeless blob on the scatterplot, the variables are likely
to be uncorrelated; for example, plot **`px`** versus **`py`**. If you see a
pattern, there may be a correlation; for example, plot **`pz`** versus
**`zv`**. It appears that the higher **`pz`** is, the lower **`zv`** is, and
vice versa. Perhaps the particle loses energy before it is deflected in
the target.
:::

Let's create a "cut" (a limit on the range of a variable):

    tree1.Draw("zv","zv<20")
    my_canvas.Draw()

Look at the x-axis of the histogram. Compare this with:

    tree1.Draw("zv")
    my_canvas.Draw()

:::{note}
Note that ROOT determines an appropriate range for the x-axis of your
histogram. Enjoy this while you can; this feature is lost when you start
using analysis scripts.[^f91]
:::

A variable in a cut does not have to be one of the variables you're
plotting:

    tree1.Draw("ebeam","zv<20")

Try this with some of the other variables in the tree.

ROOT's symbol for logical AND is `&&`. Try using this in a cut, e.g.:

    tree1.Draw("ebeam","px>10 && zv<20")

[^f91]: After this point, I won't include the `my_canvas.Draw()` line
    in future examples, and you'll have to remember to execute that
    line. I assume you've gotten into the habit of re-using or
    cut-and-pasting lines between cells.