[Yardstick]

I think that’s exactly right, but somehow to me using “an” sounds snooty even if the second syllable is accented and the “h” is silent making it grammatically correct. Doing it the other way is also grammatically correct but sounds more natural to my ears.

[Verginius Rufus]

The five-volume historical commentary on Thucydides begun by A. W. Gomme is called A Historical Commentary.... Gomme and the two scholars who completed the commentary after Gomme's death were all British. A commentary on another Greek historian by a Canadian scholar is called An Historical Commentary....