Sometimes errors can be happy accidents. Take the case of the famous delicatessen, Katz’s, on New York’s Lower East Side. When the owner, Harry Katz, explained to his signwriter that his new neon sign should say: “‘Katz’s’. That’s all” the sign came back including the throwaway instruction as “Katz’s, that’s all!” It became a much-loved, famous slogan.

However, not all mistakes are as inspired, or as welcome – as any writer, proofreader, editor or reader will know. And so the spellchecker was born in 1961, initially developed by computer scientist Lester Earnest, who worked in word processing in the 1950s. To make his first invention – computerised handwriting recognition – functional, he needed the computer to know how to spell an initial collection of the top 10,000 most common English words. As a follow-up in 1970, he asked his student, Ralph Gorin, to write a computer program called SPELL, which became the word-processing tool we all know and love – and celebrate – today. (As well as grammatical errors, the spellchecker cannot detect tone of voice or sarcasm either!)

Now surely there must be cases where the spellchecker has saved the writer from embarrassment – no doubt including Lester Earnest himself, who was inspired by his own self-confessed ‘sloppy handwriting’ and bad spelling. But most readers will wisely ask: ‘Who’s checking the spellchecker?’ after experiencing some of its notorious shortcomings:

• Some are merely comical: In his Credit and Collection Handbook, Michael Dennis warns of the spellchecker’s failure, allowing letters to go out to customers warning that ‘This litter is a final demand for payment’; or the Parish Pump Church Magazine awarding a Top 10 Misprint Competition to classics such as ‘the meeting will be gin with prayer’ or ‘Christ was revealed to destroy all the woks of the evil one…’

• Some can be costly: In the US in 2002, typos in The Franklin Report, a guide that scores architects and home-improvement services, gave three architects incorrect, low scores. Despite a profuse apology from the publishers, two of the architects threatened to sue for compensation.

Yet, despite this influx of embarrassments and threats, not all companies value the input of a proofreader as a safety net in their publications output. But, if your computer’s spellchecker is the bane of your working existence, vengeance can be relished in the Keira Knightley film, Official Secrets. Ms Knightley plays Katharine Gun, a British translator who worked for the Government Communications Headquarters in Cheltenham just ahead of the war with Iraq in 2003. She leaked a top secret memo to The Observer – it was from the American National Security Agency, asking for information on United Nations Security Council personnel in case it was needed to discredit anyone voting against the invasion of Iraq. The outraged whistleblower was arrested and charged with breaking the Official Secrets Act.

The Observer itself was caught out and discredited – in a spellchecker scandal. The copy of the leaked memo was passed to a hapless staffer who ran it through spellchecker before typesetting. The spellchecker was set to UK English, not US English. You can guess the rest. The newspaper was accused of fabricating the memo because surely if it was real, it would include American spelling! Oh, how I enjoyed that scene in the film.

So, Happy Birthday, spellchecker. We all have our own favourite examples of your work. Let us know what your highlight is.