Both reads are good. The one consistent difference seems to be on the power valve choice when a stick car is involved. From the page posted by 73440, he says to choose by 2 numbers less than vacuum reading. CUDA JAS's page says to use the half method. Holley says try both. I have 11-12ish so i picked up a 5.5. When I put that in it will take longer for the valve to open. How do you know if you want that or want it to open sooner? As for the secondary spring, it looks like it might just cover the lean spot but might not be the correct way to fix that.
