There are 10 frames for a complete walk cycle in the example above.
Preston drew the first 8, but left out the last 2 because of space in the book I assume, but it's obvious what they are supposed to be. You can figure out 9 and 10 by just reversing the positions of the arms and legs for drawings 4 and 5.
You would want to shoot the walk on 2s or inbetween it, or it will be too fast.
Here you can see that the second step corresponds to the first step. The positioning of each position is not an exact mirror image of the corresponding position. If it was, the walk would look stiff and mechanical.You'd have to shoot this on 2s as well for an 8x per step walk.
Note the perspective on the feet. The foot closest to us is always larger, and when it touches the ground is lower than the one behind when it is touching.
