It was about four hours, and 90 edits, worth of digging in the Wikipedia weeds.
Nowadays, that is a light load.
Five years after Thomsen made his first edit, 100,000 had flowed from his fingertips. A word is misspelled. A discussion page isn't categorized. A link is broken.
He's on it.
Thomsen, 74, a retired computer programmer from Fairmount, is the king of the Philadelphia Wikipedia world. With more than 120,000 edits and an eagerness to dive deep into the details of the digital encyclopedia, Thomsen spends about 10 hours each weekday behind the scenes to make the site better.
"You get caught up in this whole concept that this thing is not as well-organized as it should be, and I'm going to do better," he said.
Thomsen's edits, which put him in the top 200 of Wikipedians, escape the spotlight reserved for prolific article creators, but are crucial for the success of the site, observers said.
"The gnomes are like the cleaners that come in at night and clean the office at the business," said Mary Mark Ockerbloom, who worked for the Chemical Heritage Foundation in Philadelphia on a special Wikipedia project. "You don't necessarily see them, but, boy, if they weren't there, it'd be a different place."
Thomsen agrees. But since he suffered a stroke in January, he has begun to question whether his legacy could be more than that of a Wikignome.
"There's no point in doing more of those," he said, adding that he had been thinking of focusing on writing entries.
Many of Thomsen's early edits focused on his alma mater, Lafayette College. After graduating and serving two years in the Army in West Germany, Thomsen spent 26 years working in Philadelphia for Sunoco. He was also at various times a Republican ward chairman and president of his local civic association.
Retiring has given Thomsen, who was married 10 years ago and has no children, plenty of time to apply his computer skills to Wikipedia's 4.3 million articles.
He knows he can't mine the minutiae of Wikipedia all by himself, though. Anyone, regardless of whether he or she creates an account, can edit nearly all entries.
"I'm like a kind of missionary, kind of getting people to get involved," he said.
Thomsen even uses his attire to call for help. When he's outside the house and not at his computer, he usually wears one of the 15 blue-and-tan "Wikipedia Editor" caps he had made in South Philadelphia.
People who express interest in the cap are potential co-editors, he said, though few join him in the cause.
"You mean you're using it just like the old set of World Book Encyclopedias, and what are you paying?" he asks them.
When he ran out of the caps, he bought 15 more. Those went to Philadelphia Wikipedians who attended a picnic - or a Wicnic - he helped organize.
Jake Orlowitz, who helped with the Philadelphia picnic, said although he did not know Thomsen's particular habits, many Wikignomes simply cannot stop making edits.
"For people for whom Wikipedia consumes that kind of time, it is an absolutely addictive combination of a puzzle and a passion and a hobby, and, literally, in some cases, an addiction," Orlowitz said.
A 2012 Wikipedia study of heavy editors found many of their edits were made due to a sense of compulsion, though more edits were motivated by self-fulfillment.
With a tendency to ramble about the same historical trivia that finds its way into his entries, Thomsen several times avoided directly answering the fundamental question behind his compulsive editing:
He says he does not think he's addicted. Frequently using a computer program to accelerate editing and taking breaks during days that can involve up to 15 hours of edits, he says he finds the technical gnomish activities just plain fun.
Editing entries takes him across Philadelphia - to add photographs of every Carnegie library in the city with a fellow Wikipedian - and across the world - to a young woman in Guyana to collaborate on a series about Guyanan bridges.
Thomsen also buys into the Wikipedia credo that information should be free. He's not just a Wikignome; he's a public servant, he said.
As part of the Article Rescue Squadron, Thomsen rehabilitates weak articles that have a kernel of value.
"You got to worry about deletionists," he warned.
Jonathan Lansey, 27, who met Thomsen at Wikimania, the site's annual conference, is a fan of Thomsen's work.
"He's basically a knight in shining armor saving these poor, helpless articles that are notable but don't have sources," Lansey said.
After the July 2012 conference, Lansey was so impressed he dedicated a blog post to "Wikipedia celebrity Dthomsen8." That's Thomsen's Wikipedia "username."
Six months later, the celebrity hit a roadblock that few of the 20-somethings he edits with would understand: health problems.
A January stroke has jolted Thomsen's gnomish tendencies. Now that he's topped 100,000 edits, he says, what is to gain with a couple thousand more?
He wants the time to craft a legacy - a real, tangible legacy - and that may mean leaving Wikipedia fixing behind.
"Wikipedia is already a legacy which I feel I am already close to the top," he said. "I have other goals in life."
His wife is pushing him to spend time on other things, he said.
"Men don't like to hear things from their wives sometimes, and they hurt more when they're exactly true than when they're over the wall," he said.
With the time he does spend on Wikipedia, he wants to focus more on article creation rather than minor edits. His hope is eventually to be on the list of the top 100 article creators.
He might not have the discipline to do it, he said, but that would be a real legacy.
On Tuesday, the page for the vanquished logging town of Cross Fork, Pa., went live. He's on his way.
Contact Theodore Schleifer at 215-854-5607, firstname.lastname@example.org, or follow @teddyschleifer on Twitter.