I am with you on the timing chain comment - it's just wrong = same with assuming the direction of distributor rotation. And I agree that base timing using this method may result at pinging during a load test.
But I thought the author does a good job of describing the inter-play between vacuum, spark timing and idle-mixture. Granted that vacuum varies with RPM - but the whole point of idling is to dial RPM down as low as possible without stalling.
Absent a vacuum gauge it is quite easy to establish an idle that is both lean and late.
