The way I understand the octane selector is, (your original question, not the one you are looking for now) you set up your timing the way you want it by loosening that sideways screw that keeps the distributor from moving and time the engine perfectly using whatever method. Then set the octane selector in the middle at Zero. THEN if you want a few degrees of advance or retard, you loosen that screw and turn it a tad either way.
If my understanding is off, it's because I time my engines by ear and use HEI innards because the dwell is self adjusting based on RPM, there is no reason to ever change anything.
