This is a short video on using the "Number of Stars" as the focus measure (as opposed to HFR).
Its very simple and relies on the number of visible stars being a maximum at the optimum focus point. It may not work for everyone but works pretty well on my rig. You can give it a go very easily and see if its for you - if you use the Sims as I described in the last video you can try it on your data without wasting any imaging time.