Time machines: What does your watch know about you?

The important thing, Douglas Adams used to point out in The Hitchhiker's Guide to the Galaxy, was to know where your towel was. For, as the book noted, "any man who can hitch the length and breadth of the galaxy, rough it, slum it, struggle against terrible odds, win through, and still knows where his towel is is clearly a man to be reckoned with".

To which one can only answer: well, sure, but does your watch know where you are? Does it know how high up you are? Does it know what the temperature is? Does it know if the weather's getting better or worse? Does it know what sort of slope you're on, and how far you've travelled? And apart from all that, does it know what the time is?

You might think of a watch as something that sits on your wrist and tells you whether it's time for tea or not (just as before Douglas Adams, you might have thought towels were for drying yourself). The reality is that things have moved on: today, a watch is more like the first step to true wearable computing.

Take the Timex Ironman and the Suunto X6, which I've been looking at for the past couple of weeks. Both are chunky, plastic objects, the sort of thing that doesn't look out of place if you're in to chunky plastic things. The Timex comes with an additional strap-on package, about the size of a cigarette packet, which contains a Garmin Global Positioning System (GPS) module that can calculate your position to an accuracy of 10 metres or so.

Perhaps at this point you're thinking that you don't need to be told where you are, nor what the temperature is, or your compass heading, or the atmospheric pressure, or the slope. All those things can be found by looking around (hint: cloud formations tell you about atmospheric pressure changes). However, to dismiss these overlooks the number of people participating in active sports, or just easy recreational ones, who find such information invaluable. To a mountaineer, knowing whether it's 0C or –1C, and whether the weather's improving or worsening, can force the decision to carry on or turn back; and there are plenty of skydivers who have expressed interest in how accurately the X6 shows your altitude once you've jumped out of an aeroplane. It's the sort of thing that matters.

The Timex Ironman, equally, has the sort of functions that can be useful if you're training for the Ironman (a combination of distance swimming, cycling and running). And since it can measure maximum and average speeds, and distance covered, it's the sort of gadget that can enhance any sort of distance activity – walking and hiking, windsurfing, sailing, skiing (downhill and cross-country), riding and canoeing. (But not orienteering, at least not the competitive sort: you're only allowed a map and a compass and a straightforward watch in that. What, you'd never heard of competitive orienteering?)

The question as always with these gadgets is whether the struggle to squeeze functionality in while leaving extraneous widgets out has resulted in victory for the user, or the designer, or both. Too few buttons and you can't change anything (though the designer is pleased). Too many, and you can't scratch your ear without upsetting some setting and convincing your watch that a typhoon is on the way.

The Timex Ironman is actually closer to a standard watch, despite its GPS add-on (which can be clipped to a belt or strapped to the arm). There are three buttons around the side and two more on the top. Between these four there's enough to give you distance, top speed, average speed, lap times, and a second stored time (don't ask me; I really couldn't fathom this setting). There are also 27 pages of instructions – though probably only those relating to the GPS are essential.

The Suunto X6 is quite another proposition. Start with the manual – a fearsome thing that could almost be an offensive weapon if you hit someone with the spine. It's fist-sized, and 300 pages thick – though that's for five languages; the English one is just 60 pages.

Though frightened by the manual, I was encouraged by the watch itself. The display is large and friendly, and when it rotates to different settings (if, say, you throw the manual aside and start pressing buttons at random) the text appears to "roll" over an invisible ball. The buttons have a positive feel, and a sensible layout – the up button at the top, down at the bottom. Yes, it sounds obvious, but it wasn't obvious enough for Timex, apparently.

There's even a fearsome-looking PC interface cable, with jaws, that sucks out the details of what you've done and where you've been and can feed them into a computer. If you're feeling really proud, you can upload those to Suuntosports.com. It's a neat demonstration that this Finnish company has realised that the net can often be the missing piece of the puzzle. After all, if everyone in the pub is laughing at you showing off how your watch has a compass, barometer, altitude system, and so on, where can you be sure of finding someone who does think it's great? Online, of course.

Timex Ironman Speed and Distance: £219.99 (www.timex.com); Suunto X6: £299.95 (www.suunto.fi)