@AnCaoladoir
Oh, this is an interesting plank, it's basically "constructed wrong", as one should flip the wood, when making the plank, but this repeats. The reason for this is that if the absorbs moisture, the wood would not bent to one direction, but creating a sort of alternating wave pattern, so it keeps the form slightly better.

This is the one rare thing I remember from my woodworking class. And the reason I noticed it, was that I tought it was an interesting diffuse texture to replicate.