Friday 16 November 2007 - Altimeter vs Global Positioning System

Recent debate concerning the relative usefulness of these two bits of kit has stimulated two-penneth from me, for what it’s worth.
The Suunto Altimax weighs in at 50 gm and the spare battery is negligible in weight. I have had mine for nearly 4 years and the first battery lasted for 3 years. It’s an excellent watch and a not so effective alarm clock due to the quietness of the alarm. It gives a good indication of altitude but must be reset at frequent intervals. If you don’t do this you can go up a 2000 to 3000 ft mountain and the altimeter will record you as being up to 100 metres above the summit by the time you reach it. So you must compensate for pressure changes by frequently resetting the height at known positions, or be able to carry out complicated calculations in your head given the known change in pressure – information also given by this watch. The thermometer is useful so long as you don’t wear the watch on your wrist (I find it comfortably fits on a belt loop).
The watch gives rates of ascent and descent, and you can set it to provide all sorts of complicated logging of cumulative ascent and descent data. Apart from being tedious to set up the logging (my mind just refuses to memorise the process) the resulting data is unreliable due to the logging taking place at set intervals, and the tendency when stopped for the watch to flip between its 5 metre graduations, thereby increasing both the cumulative ascent and descent totals whilst the wearer rests. Psychologically fantastic perhaps, but factually inaccurate.
Finally, the pressure readings on the watch can be utilised to predict weather, but this is tricky if they are changing anyway due to ascent/descent. It is always worthwhile looking at this reading in the morning before setting off, as falling pressure may indicate the desirability of a lower level route or other precautions.

The Garmin GPS unit weighs in at 200 gm, and two spare AA batteries weigh as much as the Suunto watch.
It’s a wonderful piece of kit if you can work out how to use it. But the batteries only last a few hours, so even on a day walk you need spare batteries if you keep the device turned on all the time.
It has loads of functions, but the small screen can be hard to read.
Unlike the Vector, it has a compass, but it doesn’t have an alarm clock. I’m not going to reiterate its treasure trove of features here, but it does come with a 72 page manual.
So I think the GPS is fine to use and have on all day if that is all one is doing, or where spare batteries or nightly recharges are possible.
Personally I have not yet mastered that constant use of the GPS – I still prefer the comfort of a map and compass, which I can generally rely upon for a precise position. However, the GPS does these days live in my rucksack, with spare batteries, for use in any emergency and for the settling of any positional debate. Even with my sometimes wayward navigation, it rarely comes out.

So whilst the Suunto Altimax is a constant companion on the hill, and is a fantastic aid to contouring over difficult ground, the Garmin GPS is normally just a hidden security blanket. I did take the latter on the TGO Challenge this year, where I was walking alone for days at a time in a remote area, and it was useful for recording the precise positions of my wild camps. I’m glad I only had to use it for that, and I didn’t encounter any of the Military Jamming referred to here.