I recently received an email from a lady that was a bit confused with my explanation of what a SPR is-my term, of course. So being one that believes that you can always improve things, I took a look at the picture on page 3.
When I pondered on it a bit, I realized that it was the horizontal loop laying at the base of the slipped stitch from the previous row that I actually lift onto the right hand needle to be knitted.
I decided not to change the term SPR, but, I put a more clear explanation of the process in the chart key and replaced the illustration.
Here is the new picture.
This loop is made, when the purl or knit at the end of the row is forced to the left, or in the direction your are knitting, when you slip the first stitch after the turn. The “loop” is what forms the gaps.
I hope this clears things up. Who knows, I might even come up with a better illustration in the future. If I do I will post it.
Knit-tweaker
Creative Knitting - Beyond Knit and Purl 
Thanks so much for making your method of slipped short row heels available. It looks so nice and neat on the inside and outside plus NO HOLES :). I have never been happy with the wrapped or yarn over short row heel on my socks. Your method is just so amazingly easy. I’ll be using this on all my heels and toes from now on. I recommend this for anyone who doesn’t like picking up stitches for a heel flap or holes in their short rows.