Professor Kageyama's Maths Training is £14.99 delivered at Play.com
Next best price is £15.93 at The Hut.
Taken from the site :-
The foundation of Dr Kageyama's Maths Training is 100 square calculations, a method conceived by Kageyama Hidea, a Japanese elementary school principal. The DS is held side ways like a book and all answers are written using the stylus. The key principal of the software is repetition which according to Kageyama stimulates the brain. The main exercise, 100 cells maths, consists of 100 hundred simple maths problems combined into a 10 by 10 grid using the numbers at the top and side of the grid. There are however many other exercises, ranging from simple one digit math problems to slightly more complex three digit challenges.
The selection of three exercises changes every time the user advances to the next level - which happens every five days
Depending on speed and accuracy a player will be rewarded with a bronze, silver or gold medal and a listing in the top three best times for that particular exercise
The software keeps track on the days in which the users trained by rewarding them with 'tick' mark in the built-in calendar