The diamond technique for drawing face is very interesting. This method is used for mapping out the central part of the face. The diamond is longest along the centre front of the head. It is widest across the eye line. The point floats on a full front head.
Full-Front
The point across the eye will move away from the face as you turn the head. It moves off the face in the direction of the turn.
Three-Quarter Turn
The centre front points stay on the face but also move more with the turn as the forehead and chin becomes more pronounced. The whole diamond can also tilt with the head in any pose.
Profile
(Source: Bina Abling)