BY eight o'clock most mornings Chris Wooldridge will have opened, arguably, the 18 most important gates in York.

At dusk he relocks them during a three-mile walk that absorbs the city's great history.

Chris has been one of the dedicated keepers of the Bar Walls for nearly 21 years now.

We have a lot to thank him for.

About a million people stroll them every year and a recent survey revealed that it was the favourite pastime of 39 per cent of York residents.

There is something else you might like to know about Chris.

His mind is wired in a very special way, enabling him to soak up any fact or figure he chooses.

Ask Chris what day of the week you were born - be it April 5, 1963, or October 20, 1976 - and he will tell you instantly.

Inquire who was at number one in the music charts on that day and he will know.

And forget logging on to the AA's online route planner when Chris is around - he has virtually memorised the road atlas of Britain. He can recite every dual carriageway and trunk road needed to get anywhere from Aberdeen to Accrington, Yarm to Yeovil.

If you saw the film Rain Man this gift of instantly recalling certain information will be familiar. Who can forget the scene when Ray would only fly Quantas because he knew the airline had never crashed. Or when his prodigious memory beat the house in Las Vegas.

The reason for this phenomenon is that both Chris and the character played by Dustin Hoffman in the movie are autistic.

There are 535,000 people with the disability in the UK. According to the National Autistic Society, only about one in every 200 possesses an extraordinary talent (known as autistic savants) like Chris. The gift is expressed differently in individual cases.

My life has been enriched by his friendship since I was a small boy.

We would bombard him with questions on music at Sunday school where he was (and still is) caretaker.

We knew he was somehow different but were captivated by his knowledge and sense of fun. Chris loved the challenge and revelled in our acclaim.

It is etched on my mind that I was born on a Thursday and The Stylistics topped the charts with Can't Give You Anything (But My Love).

And before you start typing into Google, Chris is right. I've checked.

For reasons of his own, he has now stopped memorising the music charts - personally I blame the Cheeky Girls and Crazy Frog.

Only six per cent of people with autism have a full-time job despite often possessing the necessary skills.

A study of autistic adults revealed that they regarded finding suitable work as the one thing that would improve their lives more than anything else.

Chris, 45, is fortunate in that respect.

He was taken on in his early twenties by York council to work on the Bar Walls and recently celebrated 25 years service as caretaker at his church. Then there is the gardening, painting and rubbish clearing he does for those who request it.

Autism is a more complex disability than most. Conversations with Chris are purely one way and he lives by rigorously set routines.

Driving test nerves were not an issue for him, his dad recalls.

He was so focused on the pattern of weekly lessons that he took the test without realising. It was only when he arrived home holding a piece of paper that his father knew he could remove the L-plates. Chris had passed.

The only time I've seen him flustered is when his routines are disturbed in some way.

Contrary to public perception, autism does not always prevent an independent lifestyle.

Chris lives in his own house, drives, goes horse riding and travels alone all over Europe on package tours.

The last time we spoke he told me he was looking forward to his nephew's birthday.

He is 13, was born on a Wednesday, Chris confirms, and, oh yes, The Shamen were at number one with Ebeneezer Goode.

Updated: 09:50 Friday, October 14, 2005