You don't have to be perfect. You are going to end up somewhere around 1/2 a turn in from flush, but every motor will have a different combination of fuel, pipe, plug, ambient temperature etc. So it's not a perfect art tuning these little devils. As long as you don't mis-cue and start going too lean on the HSN you will find a good tune pretty easily. Just do it by sight. If you want to be more precise, just scrape your finger nail across the top of the needle. If it catches the lip of the copper tube on the inside - turn it out more. If it drops off the needle onto the copper lip - turn it in some, simple.