"After that, he was happy," Cunningham said.
Cunningham, 78, said immediately after the tour he went back to the battlefield's visitors center and looked up the answer. In the years since the encounter, though, he has forgotten the figure.
Cunningham, of Chambersburg, said after leaving his job as a computer programmer at Letterkenny Army Depot two decades ago he set out to find something to keep him busy during retirement.
He was quickly losing interest in other ventures when he spotted an ad for tour guides.
"I'm not a historian, but I've always loved history," he said.
Cunningham brushed up on his American history and passed a 200-question test and essay administered by the National Park Service to become a licensed guide in 1984.
He said the test primarily focused on the Civil War, although he is expected to know a little about the history of the U.S. government. The federal government began licensing guides in 1915 to ensure visitors receive accurate information.
Cunningham fell in love with the job, and from April through October he spends most days conducting tours at the battlefield.
His tours last at least two hours and hit the highlights of the park, focusing on whatever the tourist who has hired him wants to see.
Most are interested in learning about the ages of the soldiers and how many casualties there were in the famous July 1863 battle.
"Union solders were on average 22. We don't know for sure about Confederates, probably slightly older," he said.
There were 51,000 casualties, including the dead, wounded and captured Union and Confederate soldiers during the three-day battle, according to Cunningham.
Cunningham said he hopes to stay on as a guide until he's 80, or older.
"It's a job I love. I don't know how to explain it. You feel self-worth after you take a group on a tour and they thank you at the end," he said.
He said he's already looking forward to going back to work this spring in his blue shirt and blazer, part of the requisite guide uniform.
Cunningham, a World War II veteran, said his interest in history developed while he was a high school sophomore in Greencastle, Pa.
"Sophomore year, we studied ancient history. I just loved it. The best marks I made in high school were in that class," he said.
Cunningham said he is disappointed that more local people haven't been to Gettysburg.
"We're 25 miles from the turning point of the Civil War, and so many people say they have never been there," he said.
Cunningham advises visitors to arrive early at the Gettysburg National Park Service Visitor Center if they want to hire a guide. The center, at 97 Taneytown Road in Gettysburg, is open daily from 8 a.m. to 5 p.m.