In reply to daWalt:
> worth baring in mind that wearing the thing on your wrist could affect the accuracy.
Nope - at least not on Suuntos. The air pressure sensor is temperature-compensated so the barometric pressure reading is always accurate.
It's the conversion
from barometric pressure
to altitude that can be affected by ambient temperature. I'm not aware of any barometric altimeter designed for recreational/sport use that attempts to correct for that. As you've realised, the key difficulty is getting a reliable ambient air temperature reading. The upshot is that whether you wear it on your wrist or hang it off the back of your pack, it will report the same altitude - it just won't necessarily be exactly the true altitude.
That's why the manual describes how to make the correction for ambient air temperature yourself if you really need to. Even then you need to have a way to measure the current ambient air temperature, and a record of what it was when you last calibrated the device.
> sounds more useless the more you think about it.
Depends exactly how accurate you need the thing to be, really. I would be reluctant to rely on an altitude reading - barometric
or GPS - for accurate navigation in poor visibility (recognising, of course, that if you've got GPS, you should have a positional fix anyway). And do you really need an altimeter to tell you when you've got to the top of something pointy, or back to the bottom of the valley?
An altimeter watch is generally easier to keep about your person all the time - ie you just stick on your wrist and there it is - and the battery should last way longer than a GPS. Nonetheless, I think that generally speaking most people looking for a navigational aid would be better off with a low-end GPS than a barometric altimeter these days. That said, even with GPS you need to understand and work within its limitations if you plan to rely on it to keep you safe.
And like any device, both are subject to user error. I once nearly missed a "pimple on a flat plateau" Munro because my GPS was set to the wrong map datum. I was being a bit lazy with my nav and it was a misty day; it was only when the mist cleared for a few seconds that I spotted a higher point a few hundred metres away! Equally, I spooked myself quite badly one time on a misty day in Coire Leis, when the altimeter reading kept going down while I was definitely climbing upwards! It was only later that I realised that I'd managed to switch it in to barometer mode early on in the ascent. By chance the pressure and altitude readings were very similar to begin with so I hadn't spotted the change.