What is this technique at 8:40 in this video?

https://lemmy.ca/post/62946420

What is this technique at 8:40 in this video? - Lemmy.ca

How is he routering freehand such a straight line on an uneven surface? I want to do this.

That’s an interesting question. I don’t know how that’s done, and conveniently the captions all videos have to have nowadays are in the way of what I need to see. I don’t know how he stays on course.