How to create a scale for a quiver plot?

So I have recently been doing some quiver plots. I am looking for a way to generate a single quiver that would be used as a scale (1:1) of the original quiver plot.

One thought I had was to find the max of the original quiver plot, and simply plot this as a vertical quiver at some point off to the side. Which raised the question, are quiver plots scaled linearly?

I assumed they were, but I do not know for certain.

If there is a better way please share! :)

Thanks in advance.