All about barometric altimeters

Barometric altimeter screen on the Garmin Montana 600

For folks who hike and bike in mountainous terrain, tracking elevation gain can be as (or even more) important than trail miles. But while GPS is getting very accurate in terms of horizontal positioning, it is surprisingly weak at determining elevation. While it’s a bit of an oversimplification, let’s just say that it’s primarily due to the geometry of the satellite constellation and any GPS receiver involved. Add in mountainous terrain and the situation can get worse.

Enter the barometric altimeter, which is supposed to solve this. Atmospheric pressure drops as you gain altitude, allowing the change in elevation to be calculated. Unsurprisingly though, barometric altimeters are affected by changes in the weather, such as when a low or high pressure system moves in. Duh!

So is a GPS with a barometric altimeter better for tracking elevation gain? Generally yes, but it is not perfect, especially when those fronts are moving through. The manufacturers are doing a much better job these days though, with firmware that takes into account both barometric and GPS-derived elevation readings, comparing them and trying to figure out just where in the z-axis you are. Still, don’t expect perfection.

Best practices

You can improve accuracy of barometric altimeters by doing the following, which comes from an email exchange with a Garmin rep:

Make sure the unit has a calibrated barometer.  You can do this by letting the unit sit at a fixed elevation for at least half an hour with a clear view of the sky to let the elevation trend to the correct number, or manually calibrating the barometer so that the elevation is correct.  If weather is adversely affecting your altimeter (pressure is changing due to weather instead of elevation changes), you may disable it by setting the device to “fixed elevation” mode which will use GPS only for elevation data.

If you want to check the Total Ascent/Descent data fields set the track log record interval to once per second.  This records all of the elevation data used to calculate the Ascent/Descent data fields in the track log which can then be used as a good reference.

Using it for weather data

I’m not a weather expert, so I won’t go into a lot of details here, but I will say that many of the models below have the ability to record and graph ambient or barometric pressure, and some can even record pressure data with the unit turned off. UPDATE: Here’s a good post on using your altimeter to monitor weather changes.

Garmin barometric altimeter FAQs

UPDATE: I came across a few FAQs which may prove useful, especially the first one…

• How do the barometric altimeter settings effect my pressure and elevation readings?
• How accurate are the calculations when using a GPS with a pressure altimeter?
• Why can’t I choose certain data fields related to the barometric altimeter on the Trip Computer for my device?

Models with barometric altimeters

Here is a list of current handheld GPS receivers sporting a barometric altimeter (most also offer an electronic compass):

• Garmin Astro 320 dog tracking system
• Garmin Dakota 20
• Garmin eTrex 30
• Garmin fenix
• Garmin Foretrex 401
• Garmin GPSMap 62s
• Garmin GPSMAP 62sc
• Garmin GPSMap 62st
• Garmin GPSMAP 62stc
• Garmin GPSMAP 78s
• Garmin Montana 600
• Garmin Montana 650
• Garmin Montana 650t
• Garmin Oregon 450
• Garmin Oregon 450t
• Garmin Oregon 550
• Garmin Oregon 550t
• Garmin Rino 650
• Garmin Rino 655t
• Lowrance Endura Sierra
• Magellan eXplorist 610
• Magellan eXplorist 710
• Magellan SwitchUp