Wow. At first it surprised me when I typed “grammar a h” into Google’s search bar and it auto-completed with “grammar a historic or an historic.” That’s exactly what I was searching for as I proofed a press release.
What returned from betterwritingskills.com was not only a discussion of what should be used, but also a chart tracking the usage of “a historic” verses “an historic” over the last 100 years in both American English and British English.
You really can Google anything.
check it out: http://www.betterwritingskills.com/tip-w005.html