altimeter watches

1:48 p.m. on September 19, 2002 (EDT)
(Guest)

We are moderate hikers. What altimeter watches are reliable yet priced reasonablly? Casio may be less then reliable. Suunato seems more than what we need and upper end prices. thanks for any suggestions. Stan

8:17 p.m. on September 20, 2002 (EDT)
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What is your price range? In altimeter watches, like anything else, you tend to get what you pay for. The less expensive Casio/Timex altimeter watch has a tiny altitude display, is limited to 13,000 ft/4000 meters, and does not use the standard ICAO altitude-pressure curve (meaning it tends to give altitudes that are off more than others when you change altitude by more than a couple thousand feet). Remember that all pressure-based altimeters do vary in accuracy with the state of the atmosphere (meaning weather conditions and changing weather). The more expensive Casios are comparable to the Avocet and Suunto in accuracy (and price!).

The least expensive accurate altimeter watch currently available is the Avocet II. I have had an Avocet for close to 10 years now and find it to track right along with my other electronic and mechanical altimeters that are well calibrated (meaning they all suffer the same problems with weather conditions - an incoming low pressure area produces too high an altitude, and an incoming high pressure region produces too low an altitude). The Avocet will reliably give you altitude, barometer, and accumulated ascent *or* descent (not both ascent *and* descent).

The Suunto Altimax is the next least expensive altimeter watch. It omits the compass that the next one up includes (the Vertech, which I have). Starting this past January, Suunto upgraded the barometer/altimeter interface to eliminate the problem I have described on this and other sites in great detail, so the barometer display will show the correct pressure when the altitude is calibrated (as you should do as often as possible at known altitude sites, such as mountain peaks, mapped lake levels, passes, etc.) If you are willing to stick with altitude, barometer, and accumulated ascent/descent, the Altimax should be fine. The more expensive Suuntos throw in more functions (or just a fancier case, made of titanium for the Observer). Some are computer-downloadable. However, if you want heart rate in addition to altimeter functions, I would suggest the Polar S710 rather than the Suunto X6HR, Advizor, or Metron. The Polar uses the Suunto pressure module and the Suunto heart rate watches use the Polar heart rate module (both Finnish companies). Polar's software and computer interface are easier to use, particularly if you want to track heart rate for training (I used to be a competitive bicyclist in my younger days, and still find an HRM to be informative in warding off the infirmities of old age - didn't stop the Grey Beard, though).

There are other alternatives to the altimeter watches. The Brunton/Silva Sherpa has an excellent altimeter/barometer module, plus temperature, wind speed, and wind chill (the temperature for the wrist altimeters is distorted by your body temperature if you wear it on your wrist, obviously). Kestrel's 4000 has the best altimeter/barometer module I have used aside from the calibrated altimeter in my plane, plus having the same functions as the Sherpa and then some - wind speed, wind chill, temperature, dew point, relative humidity, heat stress, density altitude (useful for pilots), several others.

Also, there are the mechanical altimeters from Thommens (large, expensive, but no batteries), plus the electronic Thommens pocket altimeters (also large and expensive, plus short battery life). There are other pocket altimeters, but most are not as accurate as the Thommens, the exception being the Suunto pocket altimeter (also large and expensive).

Of course, if you want altitude without the distortions of the weather, your best bet is to get an inexpensive GPS receiver. You can find the low end models of Garmin and Magellan for under $100, sometimes as low as $50 at WalMart or Target. The altitude from a GPSR, now that SA is gone, is closer than a calibrated pressure altimeter (and I don't just say that because I am a retired GPS systems engineer). Plus the time of day readout is more accurate than any wrist watch (the GPS continuously updates your GPS receiver). True, a GPSR isn't exactly wrist-sized. But what are you after - accurate altitudes? Then get a GPSR, not a pressure-actuated altimeter. If you want small size, you will have to suffer the vagaries of the weather.

12:17 p.m. on September 21, 2002 (EDT)
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Some additional info

Suunto has probably the most extensive set of altimeter-watches (they call them "wrist computers") - 7 in what they call the "cross sports" category, 2 "snow sports (although I would consider the Altimax the general basic model, works just fine for hiking, sells sometimes for $160), 4 "marine" (includes yachting timing functions and such, one with a GPS interface), and one "golf" (links to a GPS module to tell you how far to the cup and suggests which iron to use !?!!?, plus keeping score - no more cheating). 3 have heart rate functions. Several are computer downloadable. All go to 20,000 ft or higher. I have found the battery life to be something like 6 months, if you use the logging and compass functions a lot, with Suunto's claim being 18 months. The battery is user-changeable in the field, but be sure to get their kit and change the gasket at the same time. Otherwise you get leaks into the watch from your sweat on a hot day.

Casio has several "multi-sensor" watches. They no longer make the AltiDepth, I believe, having handed it over to Timex. This is the one that has the tiny window and does not use the standard ICAO altitude-pressure curve. But it is the cheapest watch I know of that has an altitude function, sometimes on sale for less than $100. The more expensive Casios are pretty good. But a couple only go to 4000 meters/13,000 feet, not enough for a Colorado 14er or Mt. Whitney. They go for from $150 to $250, depending on model and sales.

Timex has a couple of newer versions than the AltiDepth (the AltiDepth measures depth of dive for snorkelers, to 10 meters/30 feet, as I recall - never took it below 20 feet myself). The Helix Works at $140 has compass as well as altimeter/barometer. I haven't looked at it in the field and don't know what its maximum altitude limit is.

The Avocet II lists for about $160, but is often on sale for $120-130 (Redwood Trading Post is currently selling it for $129). Good to 30,000 feet, and battery life is something like 2 years in my experience with the original Avocet (I have had mine something like 10 years). You do have to send the watch to Avocet for battery replacement if you want it properly sealed against moisture. I wear my Avocet on a neck cord to keep it from harm when shoving my arm into jam cracks. The Suunto just gets shoved into a pocket, or more usually, not taken up climbs.

Nike makes an altimeter watch for about $200. I have seen them, but never examined one inthe field.

I mentioned the Polar S710, a heart rate monitor with an altimeter function. This is more for training for runners and cyclists, but gives very good tracking of altitude, plus being computer downloadable.

Out of the watch category, there is the Brunton/Silva Sherpa (Brunton, an old-line US surveying instrument company, was bought by Silva, a Swedish compass company started by the Kjellstrom family that makes surveying instruments these days. The rights to the Silva name in North America are held by Johnson Worlwide Associates, who refused to give them up when Silva bought Brunton. So "Silva" instruments in North America are actually mde by Suunto and distributed by JWA, while Silva (Sweden) instruments are sold in North America under the Brunton and Nexus names). The Sherpa is small and on a neck cord, sold at $160. I had mine up to the top of Denali and found it to be spot on.

I mentioned the Kestrel 4000. It is a bit larger than the Sherpa and lists for about $350-400, but has lots of other functions. As mentioned previously, it has the most accurate and responsive altimeter I have used besides the one in my plane (which has to be calibrated frequently per FAA regulations to be used for IFR operations). Probably more than you want.

Suunto also has a "necklace" altimeter/barometer/watch/ compass, rather larger than their watches.

I have also seen but never used the High Gear AltiTech ($140). It appears to be much the same as the Suunto "necklace" instrument, but smaller in size.

10:05 p.m. on September 21, 2002 (EDT)
(Guest)

Hi Bill S, question for you about the GPSR, please.

Hi Bill,

I'm interested in regarding to this part about using GPSR to obtain the acurate altitute. Can you explain how GPSR work on getting the altitute? How accurate are they? If I take it to the top of a man made structure, will it still gibe me the accurate altitute?

Thanks,

Loco

"Of course, if you want altitude without the distortions of the weather, your best bet is to get an inexpensive GPS receiver. You can find the low end models of Garmin and Magellan for under $100, sometimes as low as $50 at WalMart or Target. The altitude from a GPSR, now that SA is gone, is closer than a calibrated pressure altimeter (and I don't just say that because I am a retired GPS systems engineer). Plus the time of day readout is more accurate than any wrist watch (the GPS continuously updates your GPS receiver). True, a GPSR isn't exactly wrist-sized. But what are you after - accurate altitudes? Then get a GPSR, not a pressure-actuated altimeter. If you want small size, you will have to suffer the vagaries of the weather."

8:08 p.m. on September 22, 2002 (EDT)
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GPSR altitude

A GPS receiver finds a 4-dimensional solution for its position from data derived from a set of 4 of the GPS satellites - 3 space positions and one time position. It has to do the time position because the little quartz oscillator in the typical GPSR drifts by a significant amount and an accurate space position requires nanosecond accuracy in the timing (1 nanosecond is one billionth of a second, which amounts to about 1 foot of position shift).

The coordinate system the Global Positioning System (which is what "GPS" stands for) is a rectangular (XYZ) system centered on the Earth's center, in which the X axis points out through the 0-latitude, 0-longitude point (just off the African west coast), the Y axis at right angles to the X axis points out the Indian Ocean, and the Z axis points out the North Pole. Your little pocket receiver then has to convert this XYZ position at a given time into some surface coordinate (latitude/longitude, UTM, or whatever) and an altitude. This obviously means you have to "know" the exact shape of the Earth. As you probably know, the Earth is not exactly a sphere, nor even an oblate spheroid (bulge at the equator), but has all sorts of bulges and dents. The mathematical model used for the Earth is called the "geoid". It is basically just a table of numbers giving the position in the GPS's XYZ space of where "mean sea level" is. So what your receiver does is calculate your position in XYZ space at a given time, then subtract off the "mean sea level" from your position, giving your altitude (or more correctly, "height above geoid").

Now, your pocket GPS receiver these days typically gives your position accurately to about 15 meters (45 feet) 90 percent of the time for the horizontal position. The 50 percent number is about 7 meters (20 feet). The vertical accuracy is a bit worse, for reasons I won't go into here, but the 50 percent number is about 30 feet. Now compare that to the National Map Accuracy Standard - horizontal position 1/50 inch, which is 40 feet on a 1:24,000 quad, and vertical position one half contour interval, which is about 20 feet on a typical quad with a 40 foot contour interval. But, the catch is that this accuracy applies only to "surveyed points."

Ok, so what this means is that your GPS receiver will typically be within about 30 feet of the "true" elevation, no matter what the weather. If you have a poor geometry (arrangement of visible satellites), it can be worse, but if you have a clear view of most of the sky, 30 feet error is about the worst you will see. With a barometric altimeter, the calibration is typically 10 foot intervals. A change in pressure of 0.01 inch shifts the displayed altitude by 10 feet. It is pretty typical to get changes of 0.2 to 0.3 inches during a typical daily cycle (200-300 feet), and changes of an inch are not unusual for passing storm systems, meaning a shift in indicated altitude of 1000 feet. Another weather effect is produced by the Bernoulli effect of winds blowing over a ridge or through a pass - the Venturi effect of deflecting the wind's path produces a change in speed, and that change in speed via the Bernoulli effect causes a change in pressure. So on one side of a ridge or pass you will read a different altitude from the other side of the ridge or pass. That doesn't happen with a GPS receiver.

As far as taking the receiver up a manmade structure, the accuracy will still be the same +/- 30 feet 50 percent of the time. But remember that this is the altitude the receiver is located at. You can't really measure the height of a buliding or tower with a pocket GPS receiver for several reasons. First is that at the foot of the structure, you get signal blockage and will not get an accuracy in the usual, clear-sky +/- 30 foot range. Second is, even if you did get a clear sky view, your reading at the bottom might be at one end of the accuracy range and by the time you got to the top you might be at the other end of the range, giving a likely error of 60 feet, or the height of a 4 or 5 story building. And you could fall into the outliers of the accuracy range (the 95 percent or even worse). And, no, you can't just take two pocket receivers and overcome the problem. There are ways to get cm level accuracy, but that's way beyond what could be put in a post here.

The bottom line is - for purposes of hiking, a GPS receiver will give you better and more dependable altitude numbers than a pressure-based altimeter. But both have error sources, and you should understand what they are and how to spot them and deal with them. Learn your map basics first, then play with the electronic goodies.

3:51 p.m. on September 24, 2002 (EDT)
(Guest)

Bill, Thanks a bunch. your info was very enlightening. I alt least now understand what the decisions I need to make are. Stan

11:33 a.m. on September 26, 2002 (EDT)
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Yep, Bills right on. Search for sales on GPSR's. Got my Garmin Etrex for $48.99 at

Office Depot.

4:23 p.m. on September 27, 2002 (EDT)
(Guest)

Suunto Necklace

Bill,

This is an excerpt from Suunto's specs on the necklace altimeter.

The Escape203 barometer keeps you ahead of the storm and shows the current absolute and sea level pressures, temperature as well as the barometric trend for the last 6 hours. The Escape203 features also a pressure alarm. In activated state the alarm will alert the user to pressure changes of 4 mbar/0.10 inHg over a period of 3 hours. A special feature of the Escape203 is a

12:39 p.m. on September 30, 2002 (EDT)
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Re: Suunto Necklace

Quote:

... excerpt from Suunto's specs on the necklace altimeter.

The Escape203 barometer ...

Based on this information it sounds like this product is pressure based like Suunto's watches. I am concerned with accurate readings, so I would guess you would suggest a GPS rather than this product, especially since the prices are similar? Is this rational correct?

The only significant differences between the necklace and the wrist-tops are size, "suspension" (lanyard rather than wrist strap), and a few functions. But you can find the same functions among the various wrist-top models as well.

But, how accurate do you want your "accurate readings"? If you are looking for survey-grade accuracies, then your only choice is a survey-grade GPS receiver and doing post-processing, or other survey-type approaches. The costs of this are rather high - in the tens of thousands of dollars. If you would be content with meter-level accuracy, then a differential GPS setup will work. Garmin and Magellan both have handheld receivers with WAAS built in (the Garmin Venture and Vista, for example). WAAS = Wide Area Augmentation System. This is an FAA-supported system. But at present, there are only 2 satellites providing the differential corrections, and they are hard to receive dependably throughout the lower 48, and suffer badly from the canyon-canopy problems. They are geosync SVs, so are low on the horizon for much of the US. But if you can get them you will get about 3m (10 ft) accuracy for your altitudes.

Another alternative is the USCG differential system. This gives you about 5m accuracy, but is pretty much restricted to the coasts and some inland waterways (for good differential, you should be within 300 or so miles of the reference station - the USCG and WAAS systems transmit a compilation of a number of reference stations, but USCG uses ground transmitters, while WAAS uses 2 satellites).

If you use a pocket GPSR without differential corrections, then you generally get 10-15 m accuracy in altitude. "Generally" means that you do need good geometry for the satellites for your location, but since they are always moving, you can just wait a couple hours if you have a clear sky view (if you are under canopy or in a canyon - natural or manmade - you will have to move yourself to another location). The thing here is that you do not have to know anything about the current weather situation (barometer corrections and such) to get the accuracy from the GPS - your GPSR does it just fine. There is also no problem with the variations in lapse rate with the weather - the GPS-derived altitude is based purely on geometry, no pressure variations, no pressure profile variations.

But no matter what approach you use, do not expect perfect accuracy down to the centimeter unless you use survey-grade instrumentation with post-processing. If you are happy with +/- 50 feet, then a pocket GPSR will do (but remember to watch the altitude reading for 10-15 minutes to account for those statistical outliers). If you can live with a couple hundred feet of variation day to day or errors in the pressure profile that add up to a hundred feet or so over a 1000 foot elevation change, then a pressure-based altimeter is just fine. As I said elsewhere, I often seen a 50 foot difference in altitude when returning to the trailhead during a couple hours and 2000 foot climb and descent in pressure altimeters. Watch your local Weather Channel for the barometer reading over a few hours - a change of 0.01 inches is equivalent to 10 feet of elevation change, 0.10 inches to 100 feet change, and 1.00 inches to 1000 feet of elevation change.

Short answer - depending on what accuracy level you want, a pocket GPSR is more accurate in altitude than a pressure altimeter, but not as accurate as a differential GPS receiver setup, which in turn is not as accurate as a survey-grade setup.

11:28 p.m. on December 21, 2002 (EST)
(Guest)

Re: altimeter watches - Altimeter GPS alternatives

Are the barometric altimeters in the Garmin etrex Summit and Vista comparable in performance and accuracy to the watch altimeters? What are the benefits and disadvantages of altimeter enhanced GPSs? They are not that big but they also can't be worn on the wrist (at least not very easily). Does a neck-worn GPS altimeter (or Sherpa/Kestrel 4000 for that matter) work properly even when under layers of clothing?
Thanks
MJR
---

Quote:

What is your price range? In altimeter watches, like anything else, you tend to get what you pay for. The less expensive Casio/Timex altimeter watch has a tiny altitude display, is limited to 13,000 ft/4000 meters, and does not use the standard ICAO altitude-pressure curve (meaning it tends to give altitudes that are off more than others when you change altitude by more than a couple thousand feet). Remember that all pressure-based altimeters do vary in accuracy with the state of the atmosphere (meaning weather conditions and changing weather). The more expensive Casios are comparable to the Avocet and Suunto in accuracy (and price!).

The least expensive accurate altimeter watch currently available is the Avocet II. I have had an Avocet for close to 10 years now and find it to track right along with my other electronic and mechanical altimeters that are well calibrated (meaning they all suffer the same problems with weather conditions - an incoming low pressure area produces too high an altitude, and an incoming high pressure region produces too low an altitude). The Avocet will reliably give you altitude, barometer, and accumulated ascent *or* descent (not both ascent *and* descent).

The Suunto Altimax is the next least expensive altimeter watch. It omits the compass that the next one up includes (the Vertech, which I have). Starting this past January, Suunto upgraded the barometer/altimeter interface to eliminate the problem I have described on this and other sites in great detail, so the barometer display will show the correct pressure when the altitude is calibrated (as you should do as often as possible at known altitude sites, such as mountain peaks, mapped lake levels, passes, etc.) If you are willing to stick with altitude, barometer, and accumulated ascent/descent, the Altimax should be fine. The more expensive Suuntos throw in more functions (or just a fancier case, made of titanium for the Observer). Some are computer-downloadable. However, if you want heart rate in addition to altimeter functions, I would suggest the Polar S710 rather than the Suunto X6HR, Advizor, or Metron. The Polar uses the Suunto pressure module and the Suunto heart rate watches use the Polar heart rate module (both Finnish companies). Polar's software and computer interface are easier to use, particularly if you want to track heart rate for training (I used to be a competitive bicyclist in my younger days, and still find an HRM to be informative in warding off the infirmities of old age - didn't stop the Grey Beard, though).

There are other alternatives to the altimeter watches. The Brunton/Silva Sherpa has an excellent altimeter/barometer module, plus temperature, wind speed, and wind chill (the temperature for the wrist altimeters is distorted by your body temperature if you wear it on your wrist, obviously). Kestrel's 4000 has the best altimeter/barometer module I have used aside from the calibrated altimeter in my plane, plus having the same functions as the Sherpa and then some - wind speed, wind chill, temperature, dew point, relative humidity, heat stress, density altitude (useful for pilots), several others.

Also, there are the mechanical altimeters from Thommens (large, expensive, but no batteries), plus the electronic Thommens pocket altimeters (also large and expensive, plus short battery life). There are other pocket altimeters, but most are not as accurate as the Thommens, the exception being the Suunto pocket altimeter (also large and expensive).

Of course, if you want altitude without the distortions of the weather, your best bet is to get an inexpensive GPS receiver. You can find the low end models of Garmin and Magellan for under $100, sometimes as low as $50 at WalMart or Target. The altitude from a GPSR, now that SA is gone, is closer than a calibrated pressure altimeter (and I don't just say that because I am a retired GPS systems engineer). Plus the time of day readout is more accurate than any wrist watch (the GPS continuously updates your GPS receiver). True, a GPSR isn't exactly wrist-sized. But what are you after - accurate altitudes? Then get a GPSR, not a pressure-actuated altimeter. If you want small size, you will have to suffer the vagaries of the weather.

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