Sudoku is easy to understand: All you have to do is fill in a grid with numbers. Within those constrictions, it turns out, there's a lot of room for variety, and a sudoku puzzle can be easy enough for a child or hard enough to torment a university logician.

Lately there's been a boom in computer programs and handheld devices that play sudoku. Electronic sudoku has a few advantages over the paper version: It's easy to erase mistakes, and you can have the computer warn you when you've goofed up.

It should be an easy thing to translate into a video game, but I've been surprised by how many crummy sudoku programs I've seen over the last two years. Ubisoft's "Go! Sudoku," which came out last year for the PSP, is the best of the bunch, but it has gotten some competition lately.

[naviga:font face="ZapfDingbats"]4[/naviga:font] "Carol Vorderman's Sudoku" (Eidos, for the PlayStation Portable, PlayStation 2, $19.99): Carol Vorderman's site describes her as "one of Britain's best known and loved TV personalities." In her video game she presents an assortment of sudoku-solving tutorials, and players will find her preference for low-cut dresses either fetching or annoying.

The real attraction of "Vorderman," however, is its clean, easy-to-use interface. With over 1 million puzzles, four difficulty levels and a variety of ways to solve (including timed, career and multiplayer challenges), this is a robust package that will please any sudoku addict.

GRADE: 3 Stars

[naviga:font face="ZapfDingbats"]4[/naviga:font] "Brain Buster Puzzle Pak" (Agetec, for the Nintendo DS, $19.99): "Brain Buster" also benefits from clean, readable screens, although its overall design is a little clunkier than the Vorderman game's. My major complaint with it is that it forces you to tackle puzzles in order from easiest to hardest, meaning that sudoku vets who want a stiff challenge will have to slog through dozens of no-brainers first.

What makes "Brain Buster" a bargain, however, is that it features four more puzzle types from Nikoli, the publisher that popularized sudoku in Japan. Puzzle fans who have burned out on sudoku should give "Brain Buster" a try.

GRADE: 3 Stars

[naviga:font face="ZapfDingbats"]4[/naviga:font] "Toon-Doku" (Majesco, for the DS, $19.99): "Toon-Doku" has a cute, kid-friendly gimmick: instead of filling in numbers, you're lining up tiny cartoons. Unfortunately, the pictures are so small that it's sometimes difficult to tell them apart; a lemon may look an awful lot like a pie.

"Toon-Doku" also clutters up the screen with hectic background images that too often overlap with the pictures you're trying to arrange. Fortunately, you can always switch back to more readable numerals.

GRADE: 2 Stars

[naviga:font face="ZapfDingbats"]4[/naviga:font] "Sudokuro" (Crave, for the DS, $19.99): The low-budget, low-quality publisher Crave has previously unleashed such abominations as "The Bible Game," "NRA Gun Club" and "Purr Pals." "Sudokuro," which combines sudoku and kakuro in one unplayable package, lives down to Crave's dreadful reputation.

GRADE: No stars.