Dividing a circle for a stator

[MacLaddy]

Not a homework question, I was just hoping someone could assist me with understanding some math. Actually, more accurately, I was wondering if someone could double check the math on the following website.

http://www.otherpower.com/statormold.shtml

If you scroll down you will see some explanations on how to accurately divide the circle into nine equal parts, but I believe he is doing it incorrectly. See where the "Sides, Angles, and Sines" paper is shown. Seems odd that he would be using the \sin20\deg when it is 40\deg.

Wouldn't you just do the following

\frac{\pi12}{9}~=~4.188...

Thanks for any input you can offer. I have been considering taking up this project, but if the math is wrong I may not...

[MacLaddy]

Well, I digress. I realized that I needed to figure out the "chord" for the angle, as it will not follow the arc. So I used the formula c~=~r\sqrt{2-2cos40}. That gave the same answer that he was coming up with by just multiplying \sin20~by~12.

I apologize if I posted this in the wrong section, it just seemed appropriate here due to the subject matter.

Apparently I'm missing something in my trig knowledge.