The readers' editor's job is not just about the admission of error but the correction of it, too. When the role was established at the Guardian in 1997 there was only a fledgling website, and the focus was on mistakes made in a previous edition of the newspaper. Since then there has been a growing emphasis on speedy corrections of the web versions of stories.

The Guardian has an archive of at least 1.2 million text articles alone. Readers come across errors committed more than a decade ago. And there are plenty to find. As Alan Rusbridger said in his Orwell lecture last year, "newspapers are full of errors. Not just errors, but crude over-simplifications, mistakes of emphasis, contestable interpretations and things which should simply have been phrased differently. It seems silly to pretend otherwise. Journalism is an imperfect art – what Carl Bernstein likes to call the 'best obtainable version of the truth'. And yet many newspapers do persist in pretending they are largely infallible."

The readers know that the Guardian isn't infallible but are relatively happy providing we correct errors. Sometimes, however, they look for a correction faster than we can provide one. Leslie Plommer, who has filled the role of associate editor responsible for daily corrections and clarifications for the past three years, recently wrote a new internal "operational" note that makes the guidance for web corrections clearer and therefore, we hope, quicker to implement when necessary.

One of the key points of the process is a widening of the responsibility for web corrections. Before the new guidance most requests for corrections were routed through the readers' editor's office for the sake of consistency. The total number of queries to the readers' editor's office has grown to – at the very latest count – 30,000 a year. They are not all complaints – many are comments on policies, suggestions and simple questions about the way the Guardian works – but some obvious and simple errors can languish too long.

The basic rules in the new document mean editors, section heads and senior production staff have a wider responsibility to act, if they judge that there is a clear error. This should make things easier to fix out of office hours, although it is important that editors don't feel pushed by aggressive organisations that may think they see an opportunity to reshape a story for their benefit at midnight.

As the new operational note makes clear: "Any request/complaint involving a change to our published content needs thought and verification – so please do not promise corrections to outside complainants ahead of our internal checks."

The Guardian does not believe in "invisible mending" – changing text without explaining the changes in a footnote – unless the change is minor. Here is a summary of the guidance on footnotes: "A footnote must be added to record factual errors (not small grammar items such as it's/its, they're/their), starting any day after the launch date given on the webpage dateline. But even on day of launch, we always footnote: if the web article carries a comment thread; if common sense tells you that the error is serious or controversial … ; if you know the error is about to appear in the paper/magazines, because it's too late to catch the page [before it is sent to the printers]."

It is the nature of the web that the more openness is offered, the more will be expected. Since February this year changes to Guardian articles have been tracked by News Sniffer, a website that has similarly monitored the output of BBC News online for several years.

John Leach, who runs the site, says: "When I started News Sniffer … I wanted it to be a resource for those discussing and analysing online news articles … The vast majority of changes are of course mundane, but it's common to catch things that were published before proper editing which can tell you a lot about the journalists' own ideas and biases."

An overnight story in the Guardian on the Bradford West byelection carried two factual errors that were corrected within a few hours. When the readers' editor's office opened for business a footnote was added. Production departments on deadline or in the early hours of the morning try to correct significant errors in stories, but sometimes don't have enough time to footnote. In such cases they or the readers' editor should go back later to do it.