Knife tool question

Normally when I use the knife tool I hit k, z, c with the c constraining the cut to a certain angle. I never have a problem getting it to do a 45 degree cut.

But how do I get it to do say a 30 degree cut or some other degree? It must be something simple I am missing.

From the manual

Angle constrain C
Constrains the cut to 45 degree increments.

For other angles you can add some helper geometry to cut from one vertex to another which are at the correct angle

Damn… I wonder why they wouldn’t allow you to constrain other angles… doesn’t make a lot of sense