How to: change pen size in markup

So I’ve seen a lot of threads asking how to change the pen size (also known as thickness) in the markup editor. I tried to answer the threads but they were all locked. So I’m here to spread the information, in hopes I can help some fellow Apple enthusiasts.

How to change thickness of pen line:

• After entering markup mode, zoom in on the picture you’re editing. This will make the line thinner when you zoom out. The same is true for the opposite, the more you zoom out, the thicker the line.