View Full Version : how do altimeter watches work?
Dingus Khan
05-22-2008, 05:51
this may be a simple question; i have been looking into picking up one of those altimeter watches just for kicks and realized i had no clue how they worked.
is is barometry? gps?
if it is either one of those, why don't they just display that information as well?
anyone use these? reliable? suggestions?
i have never tried one and rely on topos for specifics, but it would be a neat gadget to put on a christmas list...:D
NICKTHEGREEK
05-22-2008, 06:31
http://www.thealtimeterstore.com/howtheywork.html
GPS is more accurate assuming you have the requisite number of satellites locked up at all times.
boarstone
05-22-2008, 06:37
this may be a simple question; i have been looking into picking up one of those altimeter watches just for kicks and realized i had no clue how they worked.
is is barometry? gps?
if it is either one of those, why don't they just display that information as well?
anyone use these? reliable? suggestions?
i have never tried one and rely on topos for specifics, but it would be a neat gadget to put on a christmas list...:D
I'd do the GPS unit before an altimeter, cost wise GPS is more for the money and you get a watch as well as a altimeter/light and you can navigate w/it to boot.....
what nickthegreek said. mine is a cheap timex and is awful. you have to reset it daily and it is off by 10-30% in reporting altitude change. the better ones cost the same as a gps, so just get a gps is the way to go, imo.
4eyedbuzzard
05-22-2008, 06:38
Barometry. They all have a set and calibration function of some sort and many are temperature compensated and have a built in thermometer as well. Also most give you barometric readings and trending and also functions like cumulative altitude gained/lost, etc. Obviously you have to set/correct them when at a known altitude to compensate for constantly changing barometric pressure. For hiking purposes usually you just set them whenever they are substantially off when standing at a known location/altitude.
I had one years ago. It was a decent watch. Can't say I ever wore out the altimiter barometer function if you know what I mean, but it's a neat toy.
I don't know of any watches that utilize gps. Not enough room for all the circuitry and antennae - yet.
I don't know of any watches that utilize gps. Not enough room for all the circuitry and antennae - yet.
some handheld gps' report altimeter readings using satellite readings rather than barometric pressure... and they have ones that can strap on your wrist, although they are a bit bulky.
4eyedbuzzard
05-22-2008, 06:57
The smallest I've seen are roughly cell phone size. Guess you could strap one on your wrist.
4eyedbuzzard
05-22-2008, 07:03
http://www.engadget.com/2006/01/12/new-zealands-rakon-develops-worlds-smallest-gps-receiver/
Looks like that gps watch may be here for x-mas presents in a year or two...
https://buy.garmin.com/shop/shop.do?pID=231&locale=en_US
Not as feature rich as handheld, but has some basics. I have a pouch on my chest strap so I can reach my handheld quickly when I need it. Most places I just leave it in the car though.
http://www.engadget.com/2006/01/12/new-zealands-rakon-develops-worlds-smallest-gps-receiver/
Looks like that gps watch may be here for x-mas presents in a year or two...
Cool. :cool:
4eyedbuzzard
05-22-2008, 07:14
:cool: I like tech toys. :D
sasquatch2014
05-22-2008, 07:24
If you keep your eye out you may find one on sale that is what happened with me when i was down at Campmor and it was low enough to make me go ahead and buy. I got the base model of the Suunto its called the Vector. so far I am pleased with it. You do need to reset the known altitude when you know it or the watch can get off specially if storms are rolling in or rapid rise or drop in temp occurs. I like using the Log book functions to track my daily trip. It does take a bit to get used to where the functions are and how to use and reset them. I took the little booklet along with me on a hike or two and would read and play with it at night. Made me fall asleep extra fast. If you do this and are worried about weight just cut out the 8 other languages that the print the directions in and then its not too heavy.
I like tech toys too, but it was taking the adventure out of the hike, so I mostly don't use them anymore. I only carry my gps when I feel I need a little extra margin for safety, and then I leave it turned off until I am near the margin. ;)
Dingus Khan
05-22-2008, 22:06
thanks guys, great advice.
Like Tin Man said, i too like the adventure and probably would be fascinated but frustrated with the watch if it was not utterly reliable, simple and did not need constant resetting. interesting though, that they may come out with just that very soon... :)
for the same reason i refuse to get a nav. system in my car... the altimeter has a different appeal though cause im always counting those tiny topo lines on the map to determine % grade... an old cycling habit i guess. i love knowing the ups and downs as well as the "how fars"
thanks for the replies, WB and you guys rock as usual
The following link shows the altimeter watch I have worn for 5 years daily. I never take it off except for periodic cleaning. I used to work outside in the irrigation field and it stood up to the abuse: Suunto Observer While calibration can be a hassle, it keeps you focused on what the watch does when you care about the data. Coupling that with the fact that it doesn't change any weight concerns keeps me satisfied with this option. I believe it's as close as I need when kept calibrated and I love the real time +/- feet per minute function. That is a great measurement when it comes to knocking out a big climb or getting down to the bottom of a hill.
Duplicate post removed.- ED
I have found that GPS is not that accurate for elevation. I have been at the beach (that is very definitely at sea level) and it will tell me I’m above or below (mostly above) sea level.
take-a-knee
05-23-2008, 00:32
I have found that GPS is not that accurate for elevation. I have been at the beach (that is very definitely at sea level) and it will tell me I’m above or below (mostly above) sea level.
I've experienced the same thing. I've been told that 3 birds will give you a location fix but elevation takes four. The latest units are called WAAS enabled, and will supposedly locate much more accurately, I don't know if that helps with elevation or not.
My watch, when properly calibrated is close enough on a regular basis to aid with navigation when I have a good topo map.
gearfreak
05-23-2008, 09:04
I've used this Highgear Altitech II (http://greatescapessports.com/catalog/product_info.php/cPath/41_44/products_id/131) with complete satisfaction. Yes, it is recommended that you recalibrate the altitude daily for accuracy, but where in a day do you not cross someplace without a known elevation where you can't do this? Any altimeter will perceive changes in barometric pressure as changes in elevation, so overnight the elevation on your device can change. Be aware also that the guide books show the elevations of summits that you'll often times be skirting, so your reading will be off a bit. This device is simple to operate, lightweight (2.5 oz.) and versatile. Personally, I think a GPS is overkill for such a clearly marked trail, but that's just me. If I were to us a GPS it would be the wrist mounted Garmin Forerunner. :cool:
Two Speed
05-23-2008, 09:27
I have found that GPS is not that accurate for elevation. I have been at the beach (that is very definitely at sea level) and it will tell me I’m above or below (mostly above) sea level.
I've experienced the same thing. I've been told that 3 birds will give you a location fix but elevation takes four. The latest units are called WAAS enabled, and will supposedly locate much more accurately, I don't know if that helps with elevation or not.Depends on the constellation available; more satellites, greater accuracy. As a rule of thumb elevation is almost always less accurate than horizontal position.
Rain Man
05-23-2008, 11:05
this may be a simple question; i have been looking into picking up one of those altimeter watches just for kicks and realized i had no clue how they worked. is is barometry? gps?
if it is either one of those, why don't they just display that information as well?
I have the Suunto Vector and it does display the barometric pressure as well (though I never bother looking at that info). I think there are even two settings (American and metric?) to choose from.
I set the altimeter once or twice daily while hiking, at known elevation points. I always allow a little for "slop" afterwards, but have found it to be pretty good at "ball parking" where I am on a climb and how much more I have to go.
Rain:sunMan
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cutman11
05-26-2008, 22:25
Does anyone know the altitude change to barometric pressure change correction?, ie, we are told there is about a 3 degree change in temp for each 1000 ft of altitude change. I was wondering, for example, if you are hiking at 2000ft, and the barometric pressure changes from 30 to 29, how much does that change the altitude reading on the altimeter watch?
4eyedbuzzard
05-26-2008, 22:33
For elevations under 6000 ft or so about 1" Hg per 1000 ft is a good approximation(It's exactly 1" between 2000 and 3000 ft if sea level is at STP). It's not linear as you can see from this chart http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html .
4eyedbuzzard
05-26-2008, 23:46
So about 1000 feet?
Yep. For example, if you hike up 1000 feet in elevation the barometric pressure reading should drop by about 1" Hg.
KnowledgeEngine
05-27-2008, 05:02
In response to how do you reset the altitude when it is unknown?
You simply watch your topo map, and when you reach a spot you are sure about the altitude you reset it (IE, 50 foot marked on topo, reach the base of a cliff near one of the topo lines)
How do they work?
Just like a barometer. That is why they require the constant resets. They are basically very advanced barometers, and the constantly changing pressure systems of the weather will throw off their accuracy by a percentage of barometric pressure change over time.
cutman11
05-27-2008, 13:22
So, my point was the inverse of my question -- and if I understand the replies correctly: if you are travelling at a defined altitude, and the barometric pressure increases 1mmHG, the watch will interpret your altitude as being 1000 ft lower, even though you havent actually gained altitude.
This becomes at least part of the reason people think their watches are not very good -- they hike up a 1000 ft hill, and dont realize the barometric pressure has fallen 0.5mmHg due to the weather, and they get to the top and the watch only reads 500ft higher than when they started up the hill. They conclude the watch is defective, when actually they just need to interpret better.
So, my point was the inverse of my question -- and if I understand the replies correctly: if you are travelling at a defined altitude, and the barometric pressure increases 1mmHG, the watch will interpret your altitude as being 1000 ft lower, even though you havent actually gained altitude.
This becomes at least part of the reason people think their watches are not very good -- they hike up a 1000 ft hill, and dont realize the barometric pressure has fallen 0.5mmHg due to the weather, and they get to the top and the watch only reads 500ft higher than when they started up the hill. They conclude the watch is defective, when actually they just need to interpret better.
I believe the previous posts were using "inches Hg" scale and not the "mm Hg" scale. I don't think that the atmospheric pressure could fluctuate one inch in the time it takes to gain or lose 1000' in elevation. (unless you walked through a tornado:D)
NorthCountryWoods
05-28-2008, 15:55
The older Suunto Vector altimeter was not as accurate as the newer ones (non GPS), but I don't know why exactly. My current Suunto Advisor automatically calibrates (somehow) and seems to adjust for weather changes. It's never off by more than 10 feet on any of the peaks I hit no matter what the weather and I've done nothing to calibrate it except during the initial setup 3 years ago.
The older Suunto Vector altimeter was not as accurate as the newer ones (non GPS), but I don't know why exactly. My current Suunto Advisor automatically calibrates (somehow) and seems to adjust for weather changes. It's never off by more than 10 feet on any of the peaks I hit no matter what the weather and I've done nothing to calibrate it except during the initial setup 3 years ago.
I'm puzzled how this could work. How can the watch determine whether the altitude is changing or the barometric pressure is changing? My watch allows me to choose between Altimeter mode and Barometer mode, but eventually I will have to correct the watch if I change altitude while in Barrometer mode or too much barometric pressure change happens while in Altimeter mode.
NorthCountryWoods
05-29-2008, 06:12
I'm puzzled how this could work. How can the watch determine whether the altitude is changing or the barometric pressure is changing?
I'm as confused as you.
My watch allows me to choose between Altimeter mode and Barometer mode, but eventually I will have to correct the watch if I change altitude while in Barrometer mode or too much barometric pressure change happens while in Altimeter mode.
That was the way it was with my first one. With the current one (Advisor) it doesn't matter which mode I'm in, the altitude is always close. Watched it when at camp and the weather changes and the barometer will rise or fall and the altitude stays within that 10-20 ft window. With the old one (Vector) a weather change could bring a couple hundred foot change.
Got to get a new battery for it, but will be on the LT this weekend and will test it again and report back.
4eyedbuzzard
05-29-2008, 08:22
I'm as confused as you...
Me three. And I think we all agree as to how they work.
How could ANY barometric altimeter possibly set itself?
Any pilot reading this is equally puzzled.
Tennessee Viking
05-29-2008, 19:01
this may be a simple question; i have been looking into picking up one of those altimeter watches just for kicks and realized i had no clue how they worked.
is is barometry? gps?
if it is either one of those, why don't they just display that information as well?
anyone use these? reliable? suggestions?
i have never tried one and rely on topos for specifics, but it would be a neat gadget to put on a christmas list...:D
Altimeters are not all that accurate in my opinion. They work on the basis on barometric pressure and temperature. I was looking at a friend's altimeter at Carvers Gap and it reported being in the 4800s when its up at the 5500s.
GPS is a whole not more accurate.
In response to how do you reset the altitude when it is unknown?
You simply watch your topo map, and when you reach a spot you are sure about the altitude you reset it (IE, 50 foot marked on topo, reach the base of a cliff near one of the topo lines)
Exactly.
Or if you are lazy you don't even bother to reset. Just look at a map and observe how many feet to a summit. Glance at your watch and do some quick math in your head. Use the decreasing delta as an inspiration to the top and avoid the disappointment of multiple false summits.
hikingshoes
06-20-2009, 12:46
i set my baro.at 29.92.if it goes below that it will rain.i dont know about snow at this point,have to wait and check it this winter.
i set my baro.at 29.92.if it goes below that it will rain.i dont know about snow at this point,have to wait and check it this winter.Now I'm totally lost. What do you mean by "set"? Do you mean set an alarm to notify you when the barometer droppes below that reading, or do you mean that you set the barometer to that value? Are you saying that if the barometric pressure (adjusted to sea level) goes below 29.92 then rain is coming? I know that as a general rule a falling barometer portends unsettled weather, but that doesn't mean it will rain.
hikingshoes
06-20-2009, 23:17
yes,i set my Baro.at 29.92(value).for as the pressure dropping there is unsettled weather,and each time it dropped it did rain from a range of 29.85 to 29.76.plus im still learning too.post #24 has a good chart to go by.I also talked to a pliot and onces there in the air he set his baro.to 29.92 thats where i got my number for my baro.pressure.Id never seen the chart until i seen post#24.--Charles