Even if we take as read that you did not do such a conversion, you still explicitly claimed that the diagram showed 15-18 knots. It's there in black and white, your own words.
So explain the fact that you stated it and yet it does not show any such thing. No, I don't want you bleating about the "conversion" because I've taken as read that you are right on that matter. I do not care for the purposes of this argument what enyone claimed you did nor am I entertaining any such claims as accurate. I am only interested in two things.
Does that diagram show 15-18 knots, and did you claim it did so.