# Parametric plotting

In *Chapter 10*, we used the `calc`

package to draw Archimedean spirals in *Figure 10**.8* and *Figure 10**.9*. The syntax gets easier with a plotting package, and we get a coordinate system with axes on top.

Instead of using degrees for angles, we can use **radians**. These are an alternative means of angle measurement, happily used especially by mathematicians. Though radian values are simple numbers, we usually express them in multiples of π. For example, a right angle, 90 degrees, would be written as π/2, and 180 degrees are equal to π. We could say 180 degrees is about 3.14 in radians, but we use π. In the same way, 360 degrees equal 2π, and 1,080 degrees is 6π.

We will use radian values and labels in our next plot. For this, we switch the plotting format to radian using the following command:

\pgfplotsset{trig format plots=rad}

Now, we can use radian values for the domain of the plot, which is calculated with radian arguments...