How To: Pick an Altimeter

With altimeter technology increasingly incorporated into different pieces of equipment, we have to ask, "how reliable are they as tools for backcountry navigation?" Steve McClure, Mountaineers Board Member and Seattle Branch Navigation Committee member, recently published this review in Seattle Navigation's "Navigation Northwest".
Steve McClure Steve McClure
January 04, 2016
How To: Pick an Altimeter

Early altimeters with 19 jewels and Swiss-made movements were price-prohibitive and thus weren’t included in either The Mountaineers navigation courses or the Ten Essentials. However, with new technology emerging, the upcoming  9th edition of Freedom of the Hills  will feature map, compass, and all of the modern tools with altimeters prominent among them.

Since mountains are not two-dimensional...the altimeter is sometimes as helpful as the compass, particularly where topographic maps are available. With altitude known, point-position can often be found with only one visible feature recognized; in any other case, altitude provides a check against map and compass orientation.  - Mountaineering: The Freedom of the Hills, 1st ed. 1960, p. 79

In October, some 70 navigation students took the newly named Wilderness Navigation class (FKA Basic Navigation). The class has been updated by the Seattle Navigation Committee with input from several branches, and guided by the results of the June 2015 Navigation Summit. The course now prominently features the altimeter and lays a solid foundation for GPS use. 

How cheap can you go?

Now that Swiss jewelers are no longer needed to make an altimeter, just how cheap can we go? It’s easy to spend $130 to $350 on a Suunto Core ABC (altimeter, barometer & compass) watch. But how functional is a ~$30 Casio multi-function watch? Or cheaper still, how functional are the many, free cell phone apps?

It was a little awkward to wear three wrist altimeters and more awkward still to ask my spouse and climbing partner to wait in a snowstorm on the Muir snowfield while I recorded data. But the results are in and they are clear. The cheapos work great. I can highly recommend at least one cheap watch and a handful of mostly Android cell phone apps.

The Test

tested three wrist altimeters and six apps on my Samsung Galaxy S5 smartphone. The S5 has a built-in altimeter chip as do the latest iPhone 6 models. The apps were picked were free and strongly rated.

For wrist altimeters I used my 15+ year old Suunto Observer, a new Suunto Core, and the cheapest altimeter I could find on Amazon—the “Casio SGW300H-1AVCF Twin Sensor Multi-Function Digital Sport Watch.”

In addition to the six apps from the Android Play Store (, I performed a cursory test of three iOS apps ( with similar results. See Table 1 for tool details. In the end, tool choice made no material difference.

These tools use three, quite different methods to determine altitude. The traditional method measures atmospheric pressure, as do barometers, but calibrated in feet rather than inches of mercury (or meters vs. millibars). Since weather effects air pressure, and therefore apparent altitude, these tools must be calibrated at the start of a trip and perhaps during. I calibrated them at the trailhead to a known elevation and made no further adjustments.

Tools that determine altitude using GPS use two quite different methods. The first GPS altitude method takes the absolute position in 3D space and compares it to a math model (the ellipsoid) that approximates mean sea level. GPS technology has taught us that the sea isn’t as level as we thought and undulates considerably around the world. Using a built-in table, modern GPS units then correct for the difference between the ellipsoid and local mean sea level. Early GPS units did not make this adjustment. Perhaps this is one reason GPS units have an undeserved bad reputation for determining elevation.

The other way GPS determines altitude is to assume that you are standing on the surface of the earth (a bad assumption for pilots in flight). The tool then uses GPS coordinates to find elevations in a lookup table. An Internet connection is required so this is not practical for wilderness navigation. If the Internet is not available, these apps default to the 3D method.


Tools Comments by Author
Wrist Altimeters
Suunto Observer

This approximately 15-year-old altimeter watch has been my constant companion for a long time. The cost was about

Suunto Core ALU Pure White This is a new watch in 2015. The current Amazon cost is $220.

This is a new watch in 2015. The current Amazon cost is


Altimeter Apps Tested

Android Apps
Gaia (Android version)

$20. My go-to most-highly-recommended navigation tool for backcountry and world travel.

Accurate Altimeter
Free (ver. 1.15)

Free or $1.49. Interestingly show altitude using three different methods.

DS Altimeter

Free. Interestingly show altitude using four different methods.

Runtastic Altimeter
& Compass

Free. Very slow.
GPS Test

Free. In addition, this app gives you the detailed
status of the GPS fix including showing both GPS and Russian Glonass satellites.

GPS Essentials

Free. In addition, this app provides a wide variety of other functions including sun/moon rise/set, position, bearing, and speed


iOS Apps
Gaia (iOS version) Same comments as for Android version (above)
Travel Altimeter Lite Free
My Altitude Free


The test was simple. I took all eight tools on four trips: three at in Mt. Rainier NP (a glacier climb to Whitman Crest below Little Tahoma, a climb to Anvil Rock near Camp Muir and a hike to Mildred Point) and one hike to the summit of San Jacinto Peak near Palm Springs, CA. I took measurements along the way and then compared with a gold standard “actual” elevation based on GPS location.

While we might like to know elevation with great precision, mountain navigation is tolerant of several hundred feet of deviation. The bold topographic index lines on a 1:24000 (7.5 minute) USGS map are 200 vertical feet apart so I set two criteria for success:

  1. Each individual altitude measurement does not deviate more than 300 feet from actual. As long as all measurements are within 300 feet (150% of the distance between bold lines) of actual, you will not be more than one bold line off from the actual nearest bold line. This is not a potential 600-foot error.
  2. The average altitude measurement is within 100 feet. Ideally, the altimeters would, on average, put you on the correct bold map line.

I assumed that some of the apps or the $30 Casio special would produce material errors, especially over large changes in altitude.

Ain't Misbehavin'

For these three trips, I could not get any of the wrist altimeters or apps to misbehave, with two exceptions that I’ll address below. Each device’s worst individual reading was within my criterion of success of +/-300 ft. with the worst individual reading varying by 259 ft. On average, the tools were almost ridiculously accurate with the worst average difference being only 60 ft. This was surprising especially considering one of the trips was over two days with an elevation difference of 5400 feet.

While all the tools performed exceptionally, the GPS apps were more accurate. If the barometric altimeters had been recalibrated, as recommended for a normal trip, they would have been even more competitive.

Using GPS for elevation data tends to raise eyebrows but the data says this reputation is undeserved. The data allowed me to test this question in addition to the main topic of this paper. I compared Gaia GPS, my go-to favorite navigational
tool with actual elevation data. I was able to take 14 measurements in diverse locations from the San Jacinto Mountains of southern California to Calgary, Canada. Table 2 compares the Gaia GPS measurements against good map data.

Table 2: Gaia measures compared to topo map elevations

N= Average Difference Maximum Difference
Gaia (Android version) 10 -41 feet +101 feet
Gaia (iOS version) 4 -52 feet -136 feet

A few cautions are in order. There were two anomalies that surfaced during testing, both with wrist altimeters. On the summit of San Jacinto Peak it was below freezing. When I took the watch off my wrist to use the built-in thermometer, the temperature plummeted until it hit 35F and then shot up to over 200F. The altitude, which had shown a reasonable 10,800 ft., shot up to 27,400 ft. If anyone can explain this, please let me know. When the altimeter was back on my wrist, readings returned to normal.

The second anomaly was with the Suunto Core. This watch has large buttons that protrude. There is a locking mechanism that I had not engaged and on one trip, the buttons were accidentally pushed and the watch adjusted to the wrong altitude. I left this data out of the results.

Also, remember smartphones are fragile, power-dependent electronics so get a credible case, turn it off (or to airplane mode) between uses and have a map, compass and backup tools. Wristwatch altimeters and apps that rely on atmospheric pressure are subject to changes in weather. Keep that in mind and recalibrate when the altitude is known (map position) or recalibrate against GPS which is unaffected by weather. There were no dramatic changes in weather and I did no recalibration during the tests.

Table 3. Field test results dedicated altimeters and Android apps

Steve McClure's results for the testing of altimeter tools in Navigation Northwest - December 2015.Table 3 Note: Average and maximum deviation is the difference between the tool and the actual known elevation as determined by the Google elevation service. Where the tool uses both atmospheric pressure and GPS, each is shown with the atmospheric first followed by GPS to the right of the slash.

Take this study as a strong recommendation to add an altimeter (or two!) to your navigation tools. A cheap Casio wristwatch altimeter will run for years on one battery and if you have a smart phone, add a free app. Or, better yet, add Gaia GPS for $20 and have a world-class navigation tool in your pocket.

Steve McClure sits on the Mountaineers Board of Directors as Treasurer, chairs the Finance Committee, and sits on the Seattle Climbing, Scrambling, and Navigation committees. He is an intermediate climbing student. Contact him at .

Editor's Note: The Seattle Navigation Committee invites prospective gear reviewers to submit requests to test new navigation tools. The Committee will reimburse the reviewer for the tool and offer it to the reviewer to keep at a 50% discount. Submit your brief (1 page) review proposal to the editor. Specify your experience, committee(s) affiliation, tool, source, cost and review procedures in your proposal.

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Peter Chopelas
Peter Chopelas says:
Feb 29, 2016 09:03 PM

you should add that most touch screens often will not work when near or below freezing, particularly with cold fingers.

Michele Ritala
Michele Ritala says:
Mar 28, 2016 02:08 PM

This is a great resource, thank you! I tried using a free altimeter app for the first time on a trail using a topographic map. It was a great way to estimate my location between points. I appreciate how you shared your standards for pass/fail of the various devices.

John Gilbert
John Gilbert says:
Mar 02, 2017 08:35 AM

For suggestions for free smart phone altimeters, see this doc:

Emilia Clarkson
Emilia Clarkson says:
Mar 22, 2018 10:46 PM

Those field test results are really helpful and would be fun to test those deductions for myself. Looking forward to having a permanent gig at this. Here is a link to my webpage.

Steve McCarthy
Steve McCarthy says:
Oct 01, 2018 09:55 PM

I can vouch for the low-cost Casio watches - mine works well and just keeps going and going.

Also as of this writing, one of the benefits of Mountaineers membership is a 1 year Gaia Premium Membership.

Jim Heber
Jim Heber says:
Nov 28, 2018 10:45 PM

in general your article is very good. I suggest that you add information regarding the impact of air temperature on altitude reading with a barometric altimeter. Simply put if the air temperature is colder than normal for the altitude your at, the air will be denser than the device is programmed for which causes the altimeter to give a greater altitude difference from a reference point than actual. If the air is warmer than normal it will understate altitude differences. The altitude error on a very hot day or a cold day can be large. Aircraft pilots have standard procedures to compensate for this effect which can be found by Googling Aircraft barometric altimeter corrections for nonstandard air temperatures.The main takeaway of this is to recalibrate your altimeter more often to a known reference if the air temperature is exceptionally warm or cold for the altitude where the temperature is measured. failure to recalibrate will result in a greater than actual difference in altitude when either going up or down if the air is colder than normal. The opposite is true if the air is warmer.

Travis Prescott
Travis Prescott says:
Jan 09, 2019 11:17 PM

I opted for an electronics-free altimeter as a backup to my GaiaGPS app. Sun Company Altimeter 203 ($70 on Amazon). Keep it with my compass as part of my 10 essentials and whenever I've consulted it, it's been spot on.