The picture on the left is for the case where the coordinate system is left handed, while the picture
on the right is for the right handed case. In both pictures, the red axis at the white dot points in
the direction of increasing u, the green axis points in the direction of increasing v,
and the blue axis points in the direction of increasing w.
In the description which follows, use your left hand for the left picture and use your right hand for the right picture: Make a fist. Extend your thumbs in a thumbs-up gesture. Extend your index fingers to "make a gun" with each hand. Extend your middle fingers so that they become perpendicular to your palms. Now, at the white point, aim your thumbs in the directions of the red axes, and aim your index fingers in the directions of the green axes. If you use the correct hand with the correct picture (right with right and left with left), then your middle fingers will line up with the directions of the blue axes.