Suunto x6

11:33 a.m. on October 31, 2002 (EST)
(Guest)

I'm thinking about buying a wristop computer from suunto, the x6. Could anyone of you recommend it or are there any other (better) alternatives?
If the x6 is the best one, where can I buy it for little money (cheaper than 249 USD)over the internet?
Is the problem with the changing SEA-Level with intensive increasing of altitude (over 1000m) already fixed (the problem with the Suunto vector), or not?
I am just interested in experiences of more or less professional users with this "watch". I know it's relatively new, but in spite of this fact.

2:32 p.m. on October 31, 2002 (EST)
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Gotta ask, whaddaya mean "best"? The accuracy is the same for all the Suuntos. And yes, the problem with the SEA window appears to have been fixed, starting roughly the first of this year (2002), at least for the 3 different models I checked this year up on Denali. Since the internals of the Suuntos are basically all the same, I would expect that all couple dozen versions of the Suunto have the fix. The Avocet II and current Casio models are just as accurate.

The question is what you want in your altimeter. The only reasons for choosing among the various Suunto, Casio, Avocet, and Polar models are price and functions (Polar uses a Suunto pressure module in their altitude-reading heart rate monitors, and the Suunto models with heart rate functions use the Polar transmitter and receiver modules). The X-6 Suunto has all sorts of functions that may be of little or great use to you. If you just want to read altitude, the best for the price is the Avocet II. The Avocet also gives accumulated climb or descent and a more accurate rate of climb or descent than the Suunto. If you want a computer download from the watch, then the Suunto X6, X6HR, or S6 or Polar S710 are your choices. In the Suunto line, the Altimax and Vector are the ones that have altitude, barometer, and accumulated ascent and descent at the lowest price. The Vector adds the compass. But a lot of people like the Casio triple-sensor series better than the corresponding Suuntos.

I count 14 models in the Suunto catalog, including the golf and marine versions. Casio has 4 or 5 altimeter models, and Avocet has 1 (Avocet also has bike computers that include altimeter functions). Polar has 2 models, I believe, with altitude functions. Lots of choices, wide range of functions.

So what functions do you really need? To list a few of those available on various watches:
altitude
barometer - absolute and/or reduced (sea level)
rate of climb/descent
max rate of climb/descent
accumulated ascent and/or descent (some have both)
accumulated history of climb/descent
log of altitude at settable/non-settable recording intervals
log of barometer at settable/non-settable intervals
max altitude
min altitude
"average" altitude (can't imagine what use this is,
but my Polar HRM has it, by logging interval, too)
temperature (actually the temperature of your wrist,
since the sensor is on the watch)
difference in altitude from some chosen setting
difference in pressure since some chosen setting
various altitude, barometer, temperature alarms
compass, with/without declination setting
compass bearing tracking
stopwatch functions
countdown functions
interval timers (repetitive)
calendar
clock (some with dual time)
plastic/aluminum/titanium cases
etc
etc
etc

4:10 p.m. on November 12, 2002 (EST)
(Guest)

Bill - I Have a Question for you...

Bill,

I know you are quite knowledgeable re the Sunto wrist computers. Maybe you can answer a question for me:

I just got the Vector and have used it a few times here in the lowly white Mountains of New England. Problem is that it does not seem to be very accurate.

I calibraate it at a trail head, and it is almost 15 percent off (500 feet over a 3000 foot ascent) at the summit. This particular hike took only 3 hours, so I doubt the barometer changed that much due to wx.

Any ideas why the unit might exhibit this type of "non-linear" behavior?

BTW: To double check I recalibriated it on the summit and it read about -400 low at the trail head.

Any light you can shed would be appreciated!

cb

7:24 p.m. on November 13, 2002 (EST)
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Re: Bill - I Have a Question for you...

Short answer - this is well within the range of barometric altimeters. Not to worry, just learn how to compensate for the way nature really behaves.

Longer answer - Barometric altimeters, whether the mechanical kind like the Thommens or the electronic kind like your Suunto, Avocet, Casio, et al, operate by measuring the pressure of the air and using a conversion table to get the altitude. The conversion table almost all, if not all, the quality manufacturers use is the ICAO standard atmosphere table. Unfortunately, in real life, the atmosphere never exactly matches the standard tables. I frequently hike the local hills with several altimeters I am comparing to one another. While they usually agree to within 10 or 20 feet (most have 10 foot increments), they only rarely show the same altitude difference as the survey maps show. For example, Black Mountain (2770 feet) from the Rhus Ridge parking lot (450 feet) has registered from 2650 to 2880 feet, on ostensibly the same type of day. That's 230 feet difference out of an altitude difference of 2320 feet, close to 10 percent.

The standard atmosphere tables are derived from measurements in "free air", that is, away from influences from ground heating, vegetation, etc. When you are hiking up a trail, your altimeter is measuring the atmospheric pressure close to the ground, where the lapse rate (technobabble for the relation between altitude and air pressure) is strongly influenced by the heating or cooling of the surface, air currents which are deflected by the terrain, etc, etc. Add to that the influences of the current weather system with its mixture of warm and cold air, varying humidity (varying with proximity to vegetation and water sources, for example), and other factors. It is rare that the actual current profile of the atmosphere at ground level matches the ideal standard atmosphere tables. In practical terms, some days, you will find your altimeter indicating you have climbed more than the map indicates, and on other days, it will indicate you have climbed less. 500 feet out of a 3000 foot difference is not unheard of, although it is a little unusual. More commonly, the difference is more like 100 feet of drift per thousand feet of climb. Some days it can be right on, such as our summit day on Denali last June. I had 3 electronic gadgets with me (total of 4 ounces for the light-packing fans, all with different primary functions that happened to have an altimeter among their secondary functions). I set them for 17,200 feet before leaving our high camp. All 3 registered exactly 20,320 feet at the summit, which is the official altitude. On the other hand, one hike of Mt. Dana with my son (14 yrs old at the time) showed us 450 feet below the 13k summit in the roughly 3000 feet of climb, despite being set at the Tioga entrance station, using the official benchmark altitude. It is worse, of course, when the altimeter shows you are above the summit altitude, when you actually have several hundred feet more to climb.

But that's the real world. You can't build a barometric altimeter that measures the current lapse rate at ground level and corrects itself as you hike along. However, most days you will find that it stays closer than your 500 foot error. Now GPS receivers, on the other hand, are unaffected by the current state of the atmosphere, and the altitudes calculated with the typical geometry are typically within 40-50 feet.

6:47 p.m. on November 15, 2002 (EST)
(Guest)

Great Info!

Great info Bill. Thanks for taking the time to reply.

In playing with the Vector after the climb I described above, I noted that the SEA setting was way off, reading 34.3 vs 30.0 actual on my home barometer (I live at sea-level!). I reset the SEA and the next time I used the Vector is tracked more accurately, being about 120 feet high on a 1100 foot climb.

It was interesting, as I sat on the summit of this little peak I watched the Vector slowly gain about 80 addl feet of altitude error even though I was not moving. Wierd!

I also took my GPS (Garmin 2+) on that hike and it was more accurate (and stable) than the Vector. Too bad it is such a brick!

In any case, thanks again.

cb


Quote:

Short answer - this is well within the range of barometric altimeters. Not to worry, just learn how to compensate for the way nature really behaves.

Longer answer - Barometric altimeters, whether the mechanical kind like the Thommens or the electronic kind like your Suunto, Avocet, Casio, et al, operate by measuring the pressure of the air and using a conversion table to get the altitude. The conversion table almost all, if not all, the quality manufacturers use is the ICAO standard atmosphere table. Unfortunately, in real life, the atmosphere never exactly matches the standard tables. I frequently hike the local hills with several altimeters I am comparing to one another. While they usually agree to within 10 or 20 feet (most have 10 foot increments), they only rarely show the same altitude difference as the survey maps show. For example, Black Mountain (2770 feet) from the Rhus Ridge parking lot (450 feet) has registered from 2650 to 2880 feet, on ostensibly the same type of day. That's 230 feet difference out of an altitude difference of 2320 feet, close to 10 percent.

The standard atmosphere tables are derived from measurements in "free air", that is, away from influences from ground heating, vegetation, etc. When you are hiking up a trail, your altimeter is measuring the atmospheric pressure close to the ground, where the lapse rate (technobabble for the relation between altitude and air pressure) is strongly influenced by the heating or cooling of the surface, air currents which are deflected by the terrain, etc, etc. Add to that the influences of the current weather system with its mixture of warm and cold air, varying humidity (varying with proximity to vegetation and water sources, for example), and other factors. It is rare that the actual current profile of the atmosphere at ground level matches the ideal standard atmosphere tables. In practical terms, some days, you will find your altimeter indicating you have climbed more than the map indicates, and on other days, it will indicate you have climbed less. 500 feet out of a 3000 foot difference is not unheard of, although it is a little unusual. More commonly, the difference is more like 100 feet of drift per thousand feet of climb. Some days it can be right on, such as our summit day on Denali last June. I had 3 electronic gadgets with me (total of 4 ounces for the light-packing fans, all with different primary functions that happened to have an altimeter among their secondary functions). I set them for 17,200 feet before leaving our high camp. All 3 registered exactly 20,320 feet at the summit, which is the official altitude. On the other hand, one hike of Mt. Dana with my son (14 yrs old at the time) showed us 450 feet below the 13k summit in the roughly 3000 feet of climb, despite being set at the Tioga entrance station, using the official benchmark altitude. It is worse, of course, when the altimeter shows you are above the summit altitude, when you actually have several hundred feet more to climb.

But that's the real world. You can't build a barometric altimeter that measures the current lapse rate at ground level and corrects itself as you hike along. However, most days you will find that it stays closer than your 500 foot error. Now GPS receivers, on the other hand, are unaffected by the current state of the atmosphere, and the altitudes calculated with the typical geometry are typically within 40-50 feet.

8:59 p.m. on November 15, 2002 (EST)
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Further on the Suunto - dissolving case

The continued gain in altitude as you sat on the top is due to something called "hysteresis". Basically it is a lag in response. You can see it in most instruments. To some extent it is designed in to dampen the readings and make them more stable. If you didn't have any damping, the needle (literally for a compass or mechanical altimeter, or your car's speedometer) would overshoot, bounce back, bounce up, and continue jiggling for a while. Liquid-filled compasses have the liquid in there to minimize the jiggle that comes from the human hand holding it, as an example. Of course, the friction/fluid viscosity/electronic damping does slow the response to some extent. My opinion is that most of the electronic altimeter people have put too much damping in, and so you see the lag that you noticed.

I made an unfortunate discovery about my Vector today. I was out vetting an orienteering course for an upcoming event, and had the Suunto and another recording altimeter to measure the actual climb for the event (the official climb is computed automatically from the mapping by orienteering map programs like O-Cad). Since the venue, like almost all SF Bay Area venues, has lots of poison oak, I had slathered on Ivy Block to minimize my reaction to the stuff (for the first 50+ years of my life I never had any reaction to ivy, sumac, or oak, even though I would directly handle the stuff during trail clearing projects - then one day, after a trail project, I started reacting, and badly, too.). Anyway, as I took the Suunto off after my run through the course, I noticed that the rubberized back looked strange. It appears that some ingredient in Ivy Block dissolves the plastic/rubber of the Suunto's case. Suunto and others warn about DEET, and I am sure most of you know that DEET does a serious number on Goretex and almost all other waterproof/breathable materials. But I had never seen any comment about sunblocks, poison ivy preventatives like Ivy Block and Ivy Armor, or the ivy removal lotions like Tecnu. I have not seen any effect on other watches or on heart rate monitor transmitters. I will be talking to Suunto and others about this. In the meantime, be aware that some of the stuff we smear on ourselves can affect your wrist altimeters and other devices.

11:43 p.m. on November 21, 2002 (EST)
(Guest)

Re: Further on the Suunto - dissolving case

Bill has it right--almost. What's missing is a discussion of the temperature correction of barometric altimeters. I'm talking about the AIR temperature, not the temperature of the instrument.

Just as the ISA has a profile of pressure vs altitude, so also does it have a profile of the air temperature vs altitude. It's called the lapse rate; either adiabatic (theoretical) or environmental (empirical). Basically, the lapse rate says that at sea level the air temp should be 56 degrees and at 8000' about 31 degrees F. If the air temp is anything else, your altimeter will be inaccurate unless it features air temp correction. The Avocet and Suunto models do; most others don't, including the Casio's as far as I know.

In other words, when the air is warmer (therefore less dense) than the ISA calls for, your altimeter will be less sensitive; when it's colder, more sensitive. For example, if you leave 8000' on a 70 degree day you will have to correct your altimeter by about 700' to zero it out; climbing 2000' will result in an error of about 175' too low. If the air temp profile changes when you descend, the error will change again.

This is a big, but known, problem for aircraft. It's a total mystery for most hikers and climbers. Correcting for this problem by hand is virtually impossible. Figuring out what is going on inside your electronic altimeter becomes a real puzzle, because even those few altimeters that do correct for air temp may not do so effectively. It must be a mystery to the manufacturers, too; just try to get a straight answer out of them (except for Avocet, who do have their heads screwed on).

Glad you asked?

8:25 p.m. on November 27, 2002 (EST)
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Not quite

Quote:

Bill has it right--almost. What's missing is a discussion of the temperature correction of barometric altimeters. I'm talking about the AIR temperature, not the temperature of the instrument.

*** Actually, I said that. Note my comment about the lapse rate being affected by the temperature of the ground, since you are standing on the ground. The ground temperature affects the air temperature, hence the lapse rate.

*** Actually, a full discussion of more than the basic "actual atmosphere is different from standard atmosphere used by the wrist altimeters" is far beyond what is warranted on a board such as this. Someone really wanting to know the arcane details should study such publications as those published for pilot training or basic atmospheric science texts. While I plead guilty of oversimplification, I do not think the majority of readers are well served by delving even further into the nitty gritty.

Quote:

Just as the ISA has a profile of pressure vs altitude, so also does it have a profile of the air temperature vs altitude. It's called the lapse rate; either adiabatic (theoretical) or environmental (empirical). Basically, the lapse rate says that at sea level the air temp should be 56 degrees and at 8000' about 31 degrees F. If the air temp is anything else, your altimeter will be inaccurate unless it features air temp correction. The Avocet and Suunto models do; most others don't, including the Casio's as far as I know.

*** Not quite correct. The temperature used by Avocet, Suunto, and a few others is the temperature measured by the built-in thermometer. This is, in general, NOT the air temperature, but the temperature of the case of the instrument. This is closer to the temperature of your wrist than the air temperature, for a wrist-worn instrument. If you wear your Avocet or Suunto on the factory-optional lanyard around your neck and under your parka to keep the LCD display operating while up on Denali (as I do, for example), the temperature seen by the instrument is close to body temperature (or higher when you are pushing hard). The main correction from this is the instrumental correction, not an air temperature correction. You would need an external temperature probe that sat in the free air, away from your body's heat, or outside the tent to correct for air temperature. In an airplane, you normally have an outside air temperature guage and compute the true altitude with your E6B, although some aircraft have instrumentation to do this automatically. Among instruments that are practical for the hiker/climber/skier, the Kestrel 4000 is the only one which comes close to having true air temperature compensation, and that is because it has its temperature probe exposed to the air. But you still have to hold it away from your body for a few seconds to let it come to equilibrium with the ambient air.

Quote:

In other words, when the air is warmer (therefore less dense) than the ISA calls for, your altimeter will be less sensitive; when it's colder, more sensitive. For example, if you leave 8000' on a 70 degree day you will have to correct your altimeter by about 700' to zero it out; climbing 2000' will result in an error of about 175' too low. If the air temp profile changes when you descend, the error will change again.

**** Basically what I said, except for adding the numbers. But your example is a bit misleading. The actual correction is a bit under 600 feet from standard, if QNH is 29.92. Whether the 2000 feet of geometric climb indicates 1825 feet ascended or a different value is dependent on the actual temperature profile. It will differ according to whether you have climbed on a purely ice slope in the shade or a rock slope in the sun, and if you happen to pass through an inversion layer (possible in 2000 feet, as you may see if you go up the Mexican volcanoes, or even on Mt. Baldy near the LA Basin), you will get a still different value. I realize this sort of detail is confusing to most of the readers of this board, but the point is, you can't get this specific when the measured values depend on some intricate details of the actual situation. The most you can do is generalize to - on a hot day, you will generally register less climb on your altimeter than the geometric climb. You also did not mention the effect (nor did I, intentionally) that airflow over hilly terrain has. I have observed over a hundred foot change from leeward to windward side of a narrow saddle during high wind conditions at the same physical distance below the saddle.

*** For the purposes of answering the original question, several things in atmospheric conditions affect the accuracy of your wrist altimeter - weather conditions (such as high and low pressure regions and the actual pressure gradient in the atmosphere), the atmospheric temperature profile you experience as you walk along the ground as it differs from the ICAO table built into your altimeter, whether the altimeter is temperature compensated (in this case, the instrumental temperature compensation, as opposed to the atmospheric temperature), wind flow around terrain, and other factors. Your best approach is to re-calibrate using known altitude references, using your topographic map which you should carry with you at all times.

Quote:

This is a big, but known, problem for aircraft. It's a total mystery for most hikers and climbers. Correcting for this problem by hand is virtually impossible. Figuring out what is going on inside your electronic altimeter becomes a real puzzle, because even those few altimeters that do correct for air temp may not do so effectively. It must be a mystery to the manufacturers, too; just try to get a straight answer out of them (except for Avocet, who do have their heads screwed on).

*** First, most of the people you talk to from the manufacturers are sales reps, not technically trained people, or they have a science degree in some other field than atmospheric science and only know the little bit about operating the instrument they received in a 2 day briefing before being put on the phone desk. Don't expect them to know what is going on. At most of the companies, they are expected to answer technical questions on a whole range of products from tents to stoves to ice tools to down parkas, with the electronic altimeters being a tiny fraction of one percent of the questions - most of those being "which button do I push?" I agree that the Avocet folks have more on the ball than most other companies (NK being even more knowledgable). They are a small company, offices located just a couple miles from my house, here in Palo Alto. I have gotten to know them personally over the years and have great respect for them, Rick in particular (we've been using their bicycle gear for over 25 years and I got my altimeter from them shortly after it became available, which was a couple years after their bike computer with built-in altimeter became available).

*** Fortunately, there is a relatively easy answer. For the pilot, your plane has an OAT guage (in the vast majority of planes, leaving out ultralights and such) and a calibrated altimeter with a Kollsman window, plus you have your E6B (either mechanical or electronic), or you should have. As part of your pilot's training, you learned how to use these instruments, so it is not a big problem. For the hiker/skier/climber, the solution is, as stated in the user's manuals and on posts here and elsewhere many times - recalibrate your altimeter frequently at known altitude points (you do always have your topo map with you, don't you? Or you can use your GPSR to get closer than the altimeter reads anyway). But then again, it seems that basic map and compass skills are a big mystery to most hikers and backpackers, so maybe there is no hope.

11:59 a.m. on November 29, 2002 (EST)
(Guest)

Re: Quite

Great stuff, Bill. But like we both said, a bit over the top for most climbers and hikers. I hope more at least become aware that their electronic altimeter, despite its cost and whizzy features, isn't a substitute for map and compass skills. Neither is their GPS if they don't know how to use UTM and set the correct datum to match their maps. My mouth will drop when I come across a climber carrying a Nielsen Kellerman instrument.

September 20, 2014
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