Su Doku itself may be confusing, but as a good old pencil-and-paper puzzle in today's hi-tech times, its success is as much of a head-scratcher. It has been around since 1783 without causing the tiniest ripple beyond hardcore number buffs. Logical, it isn't. Nor is it Japanese. It was invented by Swiss mathematician Leonard Eulor, who called the game 'magic squares'. When he lost his sight in a house-fire, Eulor apparently said: 'Now I will have less distraction.' That sentiment will be familiar to millions across 55 Su Doku-crazed countries, as colleagues and spouses closet themselves to do battle with Eulor's awkward brainchild. And, yes, the numbers are baffling. Wayne Gould, the programmer who brought the puzzle to the UK late last year, has made more than $1 million since devising a Su Doku program in 1997; publisher H Bauer expects sales of its Take A Break Su-Doku and Su-Doku Selection magazines to reach 850,000 per issue; and Puzzler Media, which sells the game to the national press, has been the subject of speculation this year over a £100 million sale. But chances are that Su Doku puzzles will be joining the dusty heap of Rubik's Cubes and Segways, people will let their torn-out hair grow back, and most of the 6,670,903,752,021,072,936,960 possible Su Doku solutions will go unwritten.