How does ggplot scale_continuous expand argument work? : <p>I am trying to figure out how <code>scale_continuous()</code> <code>expand</code> argument works. According to <a href="http://ggplot2.tidyverse.org/reference/scale_continuous.html" rel="noreferrer">scale_continuous documentation</a>:</p>

<blockquote>
  <p>A numeric vector of length two giving multiplicative and additive
  expansion constants. These constants ensure that the data is placed
  some distance away from the axes. The defaults are c(0.05, 0) for
  continuous variables, and c(0, 0.6) for discrete variables.</p>
</blockquote>

<p>Since they are "expansion constants", they are not actual units. Is there any way to convert them to some actual measurement to predict the actual output? For anything except 0, I just try random numbers until it works. There must be a more proper way to approach this.</p>
