It is now nine months since we launched the Wisden 100 ratings, and in that time Test cricket has been studded with glittering performances around the globe. Yet, with over 54,000 Test innings to choose from, a place among the elite 100 has proved reassuringly difficult to come by, and in fact, only two innings - and four bowling performances - have broken into our very exclusive club. The first of these was Mark Butcher's remarkable 173 not out last August (200.8 points, 48th on the list), when England successfully chased 315 to beat Australia on the last day at Headingley. The second - and one of the most thrilling knocks of all time - was Nathan Astle's blistering 222 against England at Christchurch in March.

I will never forget the sheer exhilaration and edge-of-the-Delhi-hotel-seat excitement of those two hours. New Zealand, chasing an impossible 550 for victory, had slumped to 333 for 9 when Astle (134 not out) was joined by a limping Chris Cairns. His reaction was superhuman. Launching into the new ball, Astle plundered 111 runs from nine overs, and when he was last man out with 98 still needed, he had faced only 168 balls in his entire innings.

And yet, New Zealand still lost. At the time, I suggested that, had they won, Astle's innings would have been in the Top Ten, a remark that led some people to enquire about the weighting given for winning matches.

Astle's innings, after all, was the third and highest-rated of three command performances in a heady fortnight of Test cricket, but it was the only one that failed to secure victory. Adam Gilchrist's 204 not out for Australia at Johannesburg, and Graham Thorpe's 200 not out in the third innings of Astle's match at Christchurch were more valuable to their teams, but the conditions in which they were made were less taxing.

Even though they make up three of the four fastest double-centuries of all time, the speed of Astle, Gilchrist and Thorpe's innings cannot be taken into account. To maintain uniformity across 125 years of Test cricket, the Wisden 100 limits itself to information that is available in over 70% of all scorecards, so factors such as balls faced are omitted. When Don Bradman, for instance, scored 309 in a day in 1930, it is almost certain that his innings would have been scored at better than a run-a-ball. But we do not know that for certain, so we cannot speculate. The individual merits of each innings have to be gauged by other means.

Gilchrist's innings - while undoubtedly a great knock - is in fact the lowest-rated of the three, for the following reasons.