Tennis maths

Sports journalists who understand the associated mathematics are rarer than politicians without their hands in the till. But The Independent provides a comprehensible explanation of how young Master Murray might shoot up the world rankings:

In his sights: How Murray can catch Federer
The world rankings, updated after each tournament, are based on a rolling total accumulated over the previous 12 months. Players therefore have to "defend", or try to improve on, the points they won at tournaments the previous year. In the coming weeks Andy Murray could catch Novak Djokovic and Roger Federer, who both have significant points to defend in the clay-court season.

Current rankings
1. Rafael Nadal 14,470 pts
2. Roger Federer 11,020
3. Novak Djokovic 9,010
4. Andy Murray 8,840

Monte Carlo Masters (12-19 April)
Murray would replace Djokovic as world No 3 if, for example, the Scot was knocked out in the last 16 and the Serb lost in the quarters. In choosing to miss the event Federer will lose the 700 points he earned last year.
Points to defend: Nadal 1,000, Federer 700, Djokovic 450, Murray 150.

Rome Masters (27 April-3 May)
Djokovic's victory at the Foro Italico last year leaves him particularly vulnerable to progress by Murray.
Points to defend: Nadal 10, Federer 250, Djokovic 1,000, Murray 70.

Madrid Masters (10-17 May)
Federer, who will have lost the 350 points he earned last year through winning Estoril (which he misses this time around), also has runner-up points to defend in Madrid, which replaces Hamburg in the clay-court schedule.
Points to defend: Nadal 1,000, Federer 700, Djokovic 450, Murray 150.

French Open (24 May-7 June)
The top three all have big points totals to defend, whereas Murray needs only to reach the fourth round to improve his tally.
Points to defend: Nadal 2,000, Federer 1,400, Djokovic 900, Murray 150.

Incidentally, I managed to catch the second set of his Miami victory - extremely impressive, thoughtful tennis on his part.