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A post dated April 12, 2026, recounts how computer scientist Donald Knuth confirmed an error reported in his book Computer Modern Typefaces and sent the reporter a reward check. The author says the check recorded a reward of $1.20 in hexadecimal, equal to $2.88 in decimal, and describes receiving a separate $0.32 reward after a later report that was mostly incorrect.
A post published April 12, 2026, recounts how computer scientist Donald Knuth confirmed an error in his book Computer Modern Typefaces and sent the author a reward check. The account describes a small but well-known part of Knuth’s relationship with readers: he offers rewards for errors found in his books, and the author says the check represented $1.20 in hexadecimal, or $2.88 in decimal.
The author says the episode happened about 20 years before the post. After suspecting an error, they waited months and checked it repeatedly before reporting it, concerned they might be mistaken. They also raised the find with a local university academic, who, according to the account, was not impressed by the discovery.
The reported mistake was in Computer Modern Typefaces, part of Knuth’s Computers & Typesetting series. The author says it appeared on the book’s first numbered page, in its opening paragraph and first word. They explain that the check’s memo notation, “E1,” referred to Volume E and page 1.
The author says the check has been partly censored because Knuth is concerned that its numbers could be misused. The post also says Knuth had stopped issuing real checks years ago and instead provided a novelty certificate from the fictional Bank of San Serriffe. Several years after the first report, the author submitted another suspected error. Knuth explained why it was not an error, the author says, but awarded a further $0.32 for a suggestion included in the report.
Why Knuth’s Error Checks Endure
The account gives readers a specific example of how a longstanding reward custom can encourage careful scrutiny of technical books. Knuth’s offer, as described by the author, is not only about the amount of money: it gives readers a formal way to report possible mistakes and turns corrections into part of the record around a book.
The reported location also makes the episode memorable. The author says the error was in the first word on page one, despite the book having been read by many people. That detail illustrates why even familiar or heavily consulted works can still draw new corrections. The post does not establish how many readers encountered the error or how widely it affected the book’s use.
The second report adds a different point: a submission can be mostly wrong yet still contain a useful suggestion. In the author’s telling, Knuth explained the mistake and still sent a smaller reward for that suggestion. The episode offers a glimpse of an unusually personal correction process, while the post itself is a retrospective account rather than a newly announced policy change.
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The Check Behind the Story
Knuth is an influential computer scientist and the author of major works including The Art of Computer Programming and the Computers & Typesetting series. The source post describes his practice of rewarding people who report errors in his books, including typographical mistakes, as familiar folklore in computer science circles.
The author distinguishes Computer Modern Typefaces from Knuth’s more widely read titles, while noting that the reported error was in an unusually prominent position within that book. The check’s amount is written as “0x$1.20”; the author explains that the hexadecimal figure converts to $2.88 in decimal. The post is dated April 12, 2026, but presents the check as a story from roughly two decades earlier—not as a recent payment or newly confirmed correction.
““Donald Knuth confirmed the error I had found in one of his books and sent me the coveted check!””
— The author of the April 12, 2026 post
Details the Post Does Not Supply
The post does not give the exact date of the original report, reproduce the error itself, or provide enough information to independently check the correction. It also does not include Knuth’s correspondence or a response from him; the details about the error, check and later submission come from the author’s retrospective account.
The amount is explained through the author’s hexadecimal notation, while the check image is partly censored. The source says Knuth had not issued real checks for many years, but does not specify when that practice changed or describe the current terms of any reward. The account does not indicate that the post announces a new reward, a new edition, or a current correction to the book.
No New Check Is Announced
The source post offers a retrospective rather than a scheduled follow-up. It does not announce further action by Knuth, a new edition of Computer Modern Typefaces, or a change to the reward practice. Readers seeking to verify the episode would need the original correspondence or the book’s relevant edition; neither is reproduced in the report.
For now, the confirmed scope of the news is the publication of the author’s account on April 12, 2026. Whether the reported error was later corrected in a particular printing, and what documentation exists beyond the post, remains unspecified.
Key Questions
What is the “Knuth reward check” story?
The author says Donald Knuth confirmed an error they reported in Computer Modern Typefaces and sent a reward check about 20 years before the post was published.
How much was the check worth?
The author gives the amount as “0x$1.20” in hexadecimal, which they say equals $2.88 in decimal.
Where did the reported error appear?
According to the author, it was in the book’s first paragraph on page 1, in the very first word. The post does not reproduce the wording of the error.
Did the author receive another reward?
Yes. The author says a later report proposed an error that Knuth explained was not an error. Knuth nevertheless sent $0.32 for a suggestion included in the report.
Is this a new announcement from Donald Knuth?
No new announcement from Knuth is described. The source is a retrospective post dated April 12, 2026 about an earlier experience.
Source: hn
