🚀 go-pugleaf

I'm trying to oblique a roman font. I know the pointsize and I know the 
obliquing angle. The only example of obliquing type I have seen is in
the Blue book (Tutorial and Cookbook) in which they give an example of
a font obliqued 30 degrees:
 [12 0 6.93 12 0 0] makefont
 "The 6.93 in our last matrix above is the product of 12xtan30, so our
characters are obliqued by thirty degrees." Says the Blue Book.

I tried doing this in C:
f = 12 * tan(30);

and get 76.864, not 6.93.
Since I wasn't around when they passed out the trigonometry, maybe some
kind soul could guide me to the best way to figure out the correct value
to put in that matrix. Thanks