When I was a rather pathetic geek of a teenager, I used to pass the time during advanced mathematics AS level classes, which I had somehow fluked my way into, by developing a system of calculator cricket, using the random-number generator button. Immense charts were drawn up to reckon the probability of dot-balls, run outs, even the odds of bad weather intervening. It used to take about one hour of advanced maths to play 90 overs so during the course of a term, several Test or first-class series could be completed and that meant conjuring teams to take on each other while I was pretending to be solving quadratic equations.

What started with a straightforward Australia v England series morphed into Schoolmasters v Religious Leaders, Members of the Cabinet v Famous Belgians, People Called John v Greek Orators. And so on. Drawing up an XI was almost as much fun as playing out the series. I got a D in my exams, but would like to think that the calculator cricket proved of greater benefit in the long run.

So when the Sports Editor of The Times came up with the idea of his staff conjuring their favourite county XIs, an end-of-season academic exercise to engage all our readers who like county cricket and are just as geeky as the writers, I leapt at the chance. Given more than a century of Essex cricket from which to draw the greatest team to have worn the badge was a fascinating exercise. It enabled me to find out more about the county I fell in love with when I first saw Graham Gooch captaining the side at Castle Park, Colchester.

The shocking thing, once I started trawling the averages, was how few of Essex's finest players have come from the sides I have watched, the sides, after all, that enjoyed the only success in the county's history. We won the championship for the first time less than 30 years ago, yet were producing giants of the game for decades beforehand, which was somehow reassuring. As I read my colleague's own choices, I found that while some of them had whole XIs of world-famous names their records were not all that much better than my Essex anonymoses. We had Jack Russell, for instance. Not the Gloucestershire keeper, but an opening batsman in the 1920s who played only ten Tests yet hit five hundreds. He deserves his place in history every bit as much as a Hobbs, a Fry or a Hutton.

The mission was to pick an XI for each county to take on Mars, which hardly seems fair. Club v Country is one thing, Club v Whole Planet quite another. But maybe Mars has yet to develop a top-class cricket side. For all I know, they may have the cricketing skill of Burkina Faso. At least they should give Derbyshire a good game. The matches are to be played at home (preferably during a dry season) and over four days. Usual lunch and tea breaks apply, I presume. The only stipulation was that these players must have turned out at least 20 times for their respective counties.

Naturally, these are wholly subjective sides, based on instinct as much as science. Some writers preferred overseas players, others ran away from them; some wanted to pick only those they had seen, others saw this as a chance to do some historical research. Comparing players over a long period of time is always contentious and we are bound to have left out some excellent players. If you think we have got it wrong, let us know.

As well as the greatest teams, we were asked to name our favourite XIs. These are wholly for fun; I will accept no criticism for naming Don Topley in my favourite Essex XI. Anyone who disagrees clearly never saw him being chased across the outfield by a wild dog during an otherwise unremarkable championship match with Warwickshire. It is events such as that, as much as any five-fors and hundreds, that draw us all to this wonderful sport.

Next week, having digested every county XI listed here, Christopher Martin-Jenkins, The Times Chief Cricket Correspondent, will endeavour to select the finest county XI ever.