When it comes to the technology behind how altimeter watches work, you are limited to essentially two choices – those that calculate altitude by GPS and those that use barometric pressure.
The original altimeters (discovered by French physicist Louis Paul Cailletet) used barometric pressure to calculate altitude. While the methods for gathering barometric pressure have changed with technological advances, the calculation itself has remained constant. Most altimeter watches apply a simple formula to the barometric pressure to determine elevation above sea level. In the last few years, the invention of GPS watches has introduced a new alternative to the traditional altimeter watch. As the name implies, GPS altimeter watches us longitude and latitude to communicate position to a satellite, which in turn returns various map datum, including altitude.
If your altimeter watch is GPS enabled, the way it calculates altitude is by sending your latitude and longitude to a satellite, which likely communicates with the manufacturer and returns your altitude, among a number of other data points. Because of this GPS altimeter watches are considered to be more accurate that their barometric watch counterparts. Not having to recalibrate is one of the obvious benefits to owning a GPS enabled altimeter watch. However, one of the downsides is your position and altitude is often subject to terrain – on flat, open terrain you will have near perfect communication with the satellite. However, in mountainous terrain, particularly in a canyon or gorge, you will often have poor satellite signal, resulting in inaccurate latitude and longitude positioning. Obviously, this results in somewhat questionable accuracy of your elevation. Examples of GPS enable altimeter watches are the Forerunner 305 or the Suunto X10.
99% of altimeter watches on the market use barometric pressure to determine altitude. The calculation is very simple and can be found by googling “barometric pressure to altitude conversion”. This calculation is stored on the internal software on the altimeter watch. Because barometric pressure altimeter watches use outdoor conditions to determine altitude, the accuracy of the elevation readout is often skewed by changing weather conditions. Because of this, you need to calibrate your altimeter watch when beginning your outdoor activity, then re-calibrate frequently at known points. The mostly widely bought altimeter watch manufacturers are Suunto and HighGear.
Now that we have reviewed how GPS and barometric pressure altimeter watches function – the obvious next question is cost. While the price points for altimeter watches are varied, generally GPS enabled altimeter watches are more expensive that barometric pressure watches. That said, it is not as simple as either GPS or barometric pressure to determine cost. Manufacturing quality, feature set, and brand also can influence the price point.
Learn more about the types of altimeter watches by visiting Eddie Birdhouse’s site and learning about your altimeter watch needs.
