He goes to the Civil War battleground with graphing paper in hand and paces off the field to make maps of the various battle maneuvers judging by the placement of monuments.
When he returns home to Providence after the usual four-day trek, Deissler cross-checks his maps with written accounts of the fighting in his many books on the subject.
Deissler, a clerk in the campus mailroom, first became fascinated with Gettysburg after watching the televised series produced by Ken Burns on the Civil War, and has since logged many miles going to and from Pennsylvania.
When his interest was first piqued, Deissler vowed to visit all of the Civil War battlegrounds starting with Gettysburg, but he has not yet strayed from the site of the bloodiest battle in of the war.
"It's like you're learning history in three dimensions," said Deissler. "I thought I'd be there once and that's it. But this subject is a trap ... so many men fought there, and there are so many different accounts of what went on."
Most amazing about the battlefield is its topography. The field is flat and soldiers crossed it without cover, said Deissler, which makes it no surprise that more than 51,000 soldiers were killed, wounded or captured at Gettysburg.
The Union line of soldiers - as marked off by monuments - is shaped like a fish hook on the battlefield; the Confederate line resembles a larger fish hook around that, he said. But what occurred with individual soldiers is more interesting than what each army did there, he said.
There was Col. Strong Vincent from Erie, Pa., who led his brigade up onto Little Round Top without waiting for the command and was mortally wounded, according to Deissler.
Deissler is steadily trying to photograph statues like the one for Col. Vincent, and all 1,600 monuments, on his trips.
It is an eight-hour drive to Gettysburg, and every day there is spent walking the expansive battlefield. "I am exhausted by the end of that vacation, but I love it," said Deissler, who is trying to photograph statues, like the one for Colonel Vincent, and all 1,600 monuments during his trips.
Fall is the best time to visit because the heaviest crowds of summer have abandoned the site to return to school and work, he said.
But for the first time since the beginning of the decade, Deissler will not be among an estimated 1.5 million people who will visit the battlefield each year. This fall, he is staying home to catch up on reading about Gettysburg.
"Every time you read something on it, you realize how much you still don't know," said Deissler. "Each book leads to two or three other books."
And at home is Deissler's other passion: his five cats. Each wandered into his yard as a stray, and a few he bottle-fed from infancy.
Gettysburg is not yet in Deissler's rear view window however. He hopes to return a few more times before turning the steering wheel toward Antietam National Battlefield in Sharpsburg, Md. - Kristen Lans
For information on Gettysburg, Deissler recommends: