# how accurate is the barometer, thermometer and altimeter??



## lucawatch (Mar 21, 2012)

hi all, i have a pro trek and a g-shock with barometer and thermometer, how accurate are really they?

today i had the g-shock and checked the altitude the result was: watch -130m, the android app altimeter gived 80 meters, i was in a field. and had the watch strapped to my backpack.

thanks


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## bezgeo85 (Apr 19, 2011)

*Re: how accurate is the barometer and the thermometer?*



lucawatch said:


> hi all, i have a pro trek and a g-shock with barometer and thermometer, how accurate are really they?
> 
> today i had the g-shock and checked the altitude the result was: watch -130m, the android app altimeter gived 80 meters, i was in a field. and had the watch strapped to my backpack.
> 
> thanks


Hello my friend,

Both protrek and gshock are not accurate at altimeter function. You can always calibrate at known heights for keeping a realative good accuracy. But no matter what you do it will always loose the alti since it has not alti lock and with every barometric change due to weather changes, the watch will think that the height changes.

For baro its a different story. Its rather accurate and this shoudnt worry you since the most important at baro is the tendessy. Upcoming baro mean good weather, downcoming bad ( ofcourse not always and the most important tool at predicting tool is you and your experience)

I hope that i helped you my friend, enjoy your watches. If you want more accurate (non gps) altimeter, you should check suunto, timex, tech4o and a large plethora of brands.


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## lucawatch (Mar 21, 2012)

*Re: how accurate is the barometer and the thermometer?*

thank you for the explanation, so you you trust more the android app that uses the gps to determine your location?


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## bezgeo85 (Apr 19, 2011)

*Re: how accurate is the barometer and the thermometer?*



lucawatch said:


> thank you for the explanation, so you you trust more the android app that uses the gps to determine your location?


For determining the location yes, but a phone or a gps watch wont last long as their batteries will let you down quite soon.

It depends on what activities you need.

For short periods sport activities a gps unit or a gps watch is the dead accurate solution.

For long lasting and tough enviroments outdoors activities like hiking etc. the best solution is watches with baro based altimeters. But as you will see by many people here there is two or three things that are needed to get casio altimeters more accurate.

There are several disqussions here and its funny beqause otherwise casio makes some really tough and welldesigned watches.


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## lucawatch (Mar 21, 2012)

*Re: how accurate is the barometer and the thermometer?*

_sorry i meant, you you trust more the android app that uses the gps to determine your altitude.

what would be them 2 or 3 things that would make the _casio altimeters more accurate?


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## bezgeo85 (Apr 19, 2011)

*Re: how accurate is the barometer and the thermometer?*



lucawatch said:


> _sorry i meant, you you trust more the android app that uses the gps to determine your altitude.
> 
> what would be them 2 or 3 things that would make the _casio altimeters more accurate?


i dont know this app, i dont have adroid but i guess that it is pretty accurate, far more accurate than any baro based estimated altimeter.

The things i mentioned are these


mean sea level
alti lock
better logging functions, bigger dot displays for graphs, adjust the 5 meters step to 1 like the suunto core for example
some others? i may not know or understand since i am not an experienced abc watch user. I just try to help you here

If you see some posts here there are experienced users that show detailed opinions about altimeter accuracy.

BUT dont let this discourage you, as i told you before, it depends on what accuracy you demand. Not theoritically but practical in you real life activities.

To conclude my thoughts

the baro is good as the important thing is the tendessy
the alti will ve relative good accurate as long as you calibrate it


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## bezgeo85 (Apr 19, 2011)

*Re: how accurate is the barometer and the thermometer?*

some related posts here: (not the only)

https://www.watchuseek.com/f296/practicality-barometer-altimeter-580353.html
https://www.watchuseek.com/f296/so-...e-readings-casio-pathfinder-240-a-512605.html
https://www.watchuseek.com/f17/riseman-altimeter-505740.html

you can find here some more detailed opinions by some more experienced users


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## lucawatch (Mar 21, 2012)

*Re: how accurate is the barometer and the thermometer?*

thanks for that, was a great read.

One last question: if im sitting on any beach around the world, am i always at see level? meaning zero altitude?


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## bezgeo85 (Apr 19, 2011)

*Re: how accurate is the barometer and the thermometer?*



lucawatch said:


> thanks for that, was a great read.
> 
> One last question: if im sitting on any beach around the world, am i always at see level? meaning zero altitude?


Im really happy that i helped you my friend.

Yes, and its a good place to calibrate your altimeter ( sea level= 0 m)


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## ThomAsio (Feb 26, 2010)

*Re: how accurate is the barometer and the thermometer?*

The smartphone based GPS's I've seen aint really very accurate, they are easily 70-80 meters of. Casios _can_ be precise, provide one take care and calibrate often. Tissot T-Touch Expert is the most precise of these 3 units, it's rarely more than about 10 meters of. Without calibration.


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## xevious (Feb 1, 2008)

*Re: how accurate is the barometer and the thermometer?*

Thomas, do you have any information on how Tissot is capable of being more accurate than Protrek? Also, how would you compare it to Suunto?


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## jeepcoma (Feb 28, 2012)

*Re: how accurate is the barometer and the thermometer?*



ThomAsio said:


> Casios _can_ be precise, provide one take care and calibrate often.


Totally agree. After getting some real field experience and just wearing every day, my PRW5100 is extremely accurate. Just like any precision tool, you need to know how to use it and calibrate it to get the best results. Altitude is derived from pressure, and the pressure sensor in this model is very, very good with excellent thermal compensation. (note, I don't speak to the effectiveness of other modules, but the question was about protreks in general)

First you must start with a known altitude, or a starting reference point. From there, you can measure the change in altitude relative to that point, accepting that you're also factoring in changes due to weather conditions. The latter part is very important and affects all pressure-based altitude calculations equally, including the Suunto (they do offer more features such as enhanced reporting resolution and conveniences such as altitude lock, but do not have more inherent accuracy in the sensor). So absolute accuracy depends greatly on how fast you are ascending/descending, vs how quickly atmospheric conditions are changing.

There's a good 1 hour walking loop around my neighborhood I take frequently and I've found the 5100 to track it very consistently and accurately. My house is at 100 ft elevation so I always calibrate to that when I start off, and set the recording speed to 5 second intervals, and reset the trip history. The loop takes me down to a nearby river that's about 20 ft above sea level and I will always get a reading of 20-40 feet (depending on how high the water is and how close I get). From there it's an ascent up to about 200 feet, I get readings at the 180-200 mark. There are sections with smaller elevation changes, those under 20 feet get washed out in the resolution but in general it's very good at tracking the larger trending changes.

I do wish the resolution is better, but really only because I believe the sensor to be capable of more accuracy than was engineered in the scale (probably for sake of user friendliness and to err on the side of more stable readings). An interesting thing is the scale of altitude vs pressure: in Baro mode you're limited to seeing changes of 0.05 inHg, but in Alt you can measure 20 feet changes, which works out to about 0.025 change in inHg (I have not worked out the conversions between all the different options in meters vs feet, inHg vs bar etc to figure out which "scale" is the most granular, but it will probably bug me now to figure it out). So, if you REALLY care about tracking the pressure and you're in a fixed location, you can actually get more information out of the altimeter mode than you can the barometer! Plus, some nifty logging features and the history options. If you cared and wanted to do the conversions.


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## rouse (Apr 7, 2012)

*Re: how accurate is the barometer and the thermometer?*

most of the attention on accuracy seems to have surrounded the altimeter and the thermometer, and the practical weaknesses of these. what about the barometer? i have a pathfinder 2000 and the barometer reading seems to be about 2 kPa off (based on the local weather conditions report). the manual says that the barometer is factory calibrated and should not need calibraion. should i calibrate it manually? do other casio owners find the same thing?


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## Sedi (May 21, 2007)

*Re: how accurate is the barometer and the thermometer?*



jeepcoma said:


> First you must start with a known altitude, or a starting reference point. From there, you can measure the change in altitude relative to that point, accepting that you're also factoring in changes due to weather conditions. The latter part is very important and affects all pressure-based altitude calculations equally, including the Suunto (they do offer more features such as enhanced reporting resolution and conveniences such as altitude lock, but do not have more inherent accuracy in the sensor).


This is probably the most important part to keep in mind - it's really not a question of accuracy of the sensors - my Protreks and my Suunto show the same absolute pressure. But the implementation is very different. I got great results while on vacation just a few days ago by using the logging feature of my PAW-500. I started the recording session when leaving my home - 1st calibrating the altimeter of course. Then stopped the session when reaching my destination - all I then did was to recalibrate to the last recorded altitude stored in memory when travelling back - reaching home again the height was correct within a range of +/-5m. My Suunto X-Lander can't do any better (of course it doesn't have alti-lock either). Still I wish they at least would implement MSLP - then I can live just fine without the alti-lock (just takes a little more effort in calibrating). I have to say however that the altimeter in the X-Lander updates faster than the one in the PAW-500 - tried it once while travelling by car (I was not the driver :-d) and having one on the left and one on the right wrist.

cheers, Sedi


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## ThomAsio (Feb 26, 2010)

*Re: how accurate is the barometer and the thermometer?*



xevious said:


> Thomas, do you have any information on how Tissot is capable of being more accurate than Protrek? Also, how would you compare it to Suunto?


I havent tried a Suunto, they're not my cup of tea. I've been through several of the Suunto manuals though. I _think_ several Suunto's get around the problem with a manual alti lock, which of course is no better than if the user remember to turn it on and off. They also have sealevel compensation - which basically just is a calculation of what the air pressure would be at sealevel, despite one being up in, say, the mountains. The major advantage of this, is they _can_ be easier to calibate - provided one have the actual local sealevel pressure from another source.

Other Suunto's seems to do what the T-Touch Expert also do: They simply measures airpressure very often, I guess it's about once each 5 minutes or so, and if they registrer a fast pressurechange, they consider it a altitude change. And slow changes are considered a weatherchange. A challenge here, is if the weather suddenly get very rough fast - then the barometer change can be dramatically, but the watch usually will consider it a altitude change. The T-Touch Expert have the option of choosing a climate zone, which I believe will increase the watch ability to interpret these changes correctly. Dont know about Suunto.

I dont think T-Touch II have this kind of baro locks. A downside of these constant pressure measurings, is battery drain, and I'll bet that's why Casio havent made such things - they swear to solar... I'm still on my first battery in my Expert (13-14 months now), and have no clue on how long it will last. But I wouldnt mind to have the option of disabling the auto altimeter lock, in order to save battery.

But no matter what, all of these relatively simple barometers found in wristwatches, all share one problem: If you change altitude simultanously with a pressure change due to weather, the watch can only do it wrong - likely for oth alti and baro, if you are lucky, it only fails in one category ;-)


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## Sedi (May 21, 2007)

*Re: how accurate is the barometer and the thermometer?*



ThomAsio said:


> They also have sealevel compensation - which basically just is a calculation of what the air pressure would be at sealevel, despite one being up in, say, the mountains. The major advantage of this, is they _can_ be easier to calibate - provided one have the actual local sealevel pressure from another source.


You can also calibrate it using a know altitude and it will then calculate the current sea-level pressure based on absolute pressure and temperature. So you need only either one of those values to calibrate it exactly.

cheers, Sedi


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## dmmartindale (Mar 26, 2010)

*Re: how accurate is the barometer and the thermometer?*

You may be comparing your Casio (which reports "station pressure", the pressure at the watch location) with a pressure that has been adjusted to sea level. Pressure values from weather stations and airport control towers are adjusted to sea level, not local pressure.

Some watches display sea level pressure. You may be able to get them to display local pressure by setting the altitude to zero. Some altimeter watches can display both pressures at the same time. Make sure you are comparing to a station pressure value.

I have two Casio altimeter watches. One agrees with all my other altimeters, within 1 mbar, when all are displaying local pressure. The other watch is about 4 mbar off.

Dave


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