For navigation, orientation, proper map use and hiking and trail-running in general, calculating current altitude, elevation gain and elevation loss is as important as distance. For sport purposes, getting in our weekly elevation dose in preparation for a races is just necessary. This is how we can measure readiness and preparedness for a certain type of course.
For hiking, this is how we can know where we are for instance on a course and where we have to turn left or right. Yeah when you have a map and use that only for navigation with compass, that might work as well. However, I used to live in Ireland, where there is no signposting, flashes or markers and no real tracks or trails. You just walk in the bog all day long. A well working altimeter would give you the third axis to your positioning. Map, compass and a barometric altimeter.
So a barometer is an air-pressure / atmospheric sensitive device giving your data in milibars or hectopascal. Then a device like a digital altimeter, calculates this, or you can adjust yourself manually in digital or analog devices too.
They are all superbly precise. However the change in air pressure can occur not only when ascending and descending, but when meteorological changes happen, like a cold front or a storm is coming. This is where the GPS technology and an auto-adjusting altimeter comes in. I am not sure in what manner it really works, but it works. It just uses both in a twin mode, but not sure which one is used more often nor which is superior the other.
In the Suunto devices it is called FusedAlti in Garmin there is no special name to it, just auto calibrating altimeter. I have been using the Garmin Fenix 3 for almost 16months, I have never came across any anomalies, if GPS reception was also correct. Nor did I experience problems with the Ambit 2 & 3 or the Spartan Ultra.
Altimeters exist for a very long time and I think the technology is pretty much mastered.
This is what our small video and test shows too, that outside of a couple of meters of non-significant difference we do not have any major distinctions between the two watches if the altimeter was adjusted at the beginning of our 'outing' and GPS reception was correct all the way.
We adjusted manually the altimeters to 11m, what is a reference taken from a topographic map of IGN , what is the French National Geographical Institute, so probably quiet reliable. We had to do this as the auto-calibrating GPS alti was giving like 37m of elevation, while the reality was only 11m.
I wrote down on a piece of paper some other reference altitudes, what we double checked, to see that after an initial measure, arriving back to the exact same spot, how these altimeters would behave. Nothing shocking happened outside of a couple of meters of deviation.
I also had an analog altimeter with me to make sure nothing strange happens in this particular measure. At the beginning there was some GPS referencing issue in the watches, but they readjusted it just fine and when arrived to our topographic checkpoints, they were always okay.
Finally, at the arrival point where we measured and calibrated 11m altitude at the beginning, 2,5
hours later both watches have shown 7meters what is not that bad. The weather was quiet unstable, with clear skies and clouds switching over.
Enjoy your watches for mountain use and have fun with them. The storm alarm function in the Fenix 3 is available and works just fine, while the rate of pressure drop per hour is also manually adjustable. In the Spartan , not yet, but will be coming soon !