I am indebted to Peter Biddlecombe, the Sunday Times crossword editor, for the answer to my question last month about the origins of the convention that crossword grids must be symmetrical. The rule was established by one Margaret Farrar (née Petherbridge) in the 1920s.

As we approach the centenary year of what is generally accepted to be the first modern crossword (published by the New York World on Sunday 21 December 1913) crossword groupies are likely to know the name of Arthur Wynne, the Liverpudlian who devised that original 'word-cross' puzzle. But few will have heard of the American woman who did infinitely more than our Arthur to give the modern crossword its shape.

Margaret Petherbridge originally had no particular interest in puzzles, crossword or other. She was just, accidentally, the right person in the right place. Born in 1897, she was secretary to the editor of the New York World when she was asked to help Arthur Wynne with his proofreading. Then she started setting the odd puzzle herself and seems quickly to have become better at it than he was and to have taken over.

In 1924 two recent graduates of New York's Columbia School of Journalism decided that they would rather go for publishing than for journalism. Looking for their first book, they gambled on a collection of puzzles that had appeared in the New York World. They asked Margaret Petherbridge to edit it for them. She agreed. Their names were Simon and Schuster.

The Cross Word Puzzle Book was a massive best seller. It launched the duo on their careers as book publishers and, overnight, it turned the crossword puzzle into a coast-to-coast sensation. When Margaret Petherbridge Farrar died in 1984 she was working on her 134th crossword puzzle book. In 1942 she had become the first ever crossword editor of the New York Times, which had held out against tide until then, when it risked a Sunday puzzle (only going daily in 1950). She retired from the Times in 1968.

In the course of this unintended career Margaret developed today's standard crossword grid: square, rather than any old shape; with a number before each clue and a letter count in brackets at the end; the number of black squares in a grid to be limited; grids to be an odd number of squares by an odd number of squares (eg 15 x 15 or 13 x 13), so as to have one focal square at the centre; no solution to be less than a three-letter word; multi-word solutions and solutions covering more than one box in a grid to give room for interesting phrases; and, above all, grids where the pattern of white and black squares had to be symmetrical, in order to create visual appeal.

When the crossword finally crossed the Atlantic in a big way in the late 1920s the grid design features that Margaret had persuaded the United States to follow were also imported without question.

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This is advance notice that Araucaria's special Christmas offering will be published on Saturday 22 December, with a deadline for entries of Thursday 3 January and the solution given on Friday 4 January.

Also, for those who missed the original transmission, Radio Four is repeating on Boxing Day the 24 November Archive Hour programme in which Lynne Truss explores crosswords in the BBC sound archives and talks about what crossword puzzles have meant to her.

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May I pass on two hints for when you are having difficulty with the Guardian crossword site? First, there seems to be a bug affecting those of you using certain versions of Internet Explorer as you browser. It does not seem to affect other browsers, like Safari, Firefox or Google Chrome.

The technical staff is trying to locate the bug and to deal with it but, meanwhile, it would be worth trying another such browser. Second, there are several routes from the crossword home page to your chosen puzzle. You can, of course, click on a particular puzzle along the top or down the left-hand side; but you can also use either the top or bottom half of the archive search tool. For example on 3 December, when it seemed as if the new December Genius puzzle had not been uploaded, it was in fact in the system and could be accessed by going for Genius + December or Genius + the serial number (in this case 114, since November's puzzle was No 113).

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November's Genius puzzle (No 113 set by Crucible) only got nine correct entries on the first day and 220 by the deadline. (The slow start was probably explained by the fact that the last three down clues were initially uploaded wrongly.) Despite this handicap Dave H. was in at 02:15, followed by Jeremy G. at 04:30.

Congratulations to Janice Hauser, who is November's winner.

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We hope you enjoy our crossword service. If you have any technical problems with it, please email userhelp@guardian.co.uk . If you have any comments or queries about the crosswords, please email crossword.editor@guardianunlimited.co.uk .

For Observer crosswords please email crossword.editor@observer.co.uk