Manifold and vaccum plumbing

[WorkinLonghorn]

The 34 total doesn't include vacuum advance.That(total advance) is what you get with initial (say,10 degrees) plus max centrifugal advance (perhaps 24 degrees). 10+24 would be 34 total advance at high engine RPMs.They sometime specify that you plug off the vacuum line while checking these figures.
BUT for every-day driving which includes part throttle and cruise conditions,the engine can take much more advance and will reward you with better performance and much better economy.Thus the Vac Advance which is only a factor during PART throttle.
Think about it this way; when you are cruising along at 1/8 throttle,only a small amount of air/fuel is entering the cylinders and so the "compression ratio" is very low,maybe 4-1 or something.Therefore if you start the spark earlier,the slow-burning,low compression charge will produce it's power at the optimal point in the cycle.