Based on the PocketPC operating system, the Cassiopeia E-115 is a chunky piece of button-laden electronics that begs to be picked up and played with. It has a 16-bit colour screen which, at 240x340 pixels, is the largest of the five devices on test. Below the screen is a directional button for scrolling through lists and fields, and dedicated buttons for calling up the menu, the calendar and your contacts book.

Turn the unit sideways and you'll find more buttons running down the left hand side. As well as the on/off switch, there's a button which triggers PocketPC's Windows-like Start menu and a thumbwheel Action Control for scrolling and selecting. These two controls pretty much enable you to navigate the entire system with one hand without having to remove the stylus from its holder until you decide to enter new data.

Unusually, Casio provides its own Mobile Calendar and Address Book in place of Microsoft's Pocket Outlook. Otherwise, you still get the standard PocketPC applications: Word, Excel, Money, Internet Explorer and the e-mail inbox from Outlook. You can also make good use of the media players for MP3 audio and MPEG video thanks to the generous 32MB of memory built into the machine as standard. This can be expanded via the Compact Flash slot in the top. There's even a stereo headphone jack so you can use the Cassiopeia E-115 as an MP3 player.

The real star of the show, though, is the screen, which is bright and super-clear. Just bear in mind that the device weighs about a quarter of a kilo, and battery life is just six hours. But the Cassiopeia E-115 is so desirable you might not care.