The lay direction is determined by the direction the machine is turning during the stranding operation. The conventional method to determine the lay direction is to observe the upper surface of the stranded conductor with one end pointing toward you and the wire leading away from you:

If the strands turn left leading away from the observer and have the same slant as the middle of the letter "S", the convention denotes an "S" lay direction.

If the strands turn right leading away from the observer and have the same slant as the middle of the letter "Z", the convention denotes a "Z" lay direction.
Lay