Suunto Altimeters, can you help?

1:45 a.m. on May 22, 2002 (EDT)
(Guest)

My old watch died and bought Xlander as a treat to myself.

We live only 650 meters above sea level but I find everynight my house can move upto 100 meters up or down which concerns me.

If I manually adjust the height then the barometer is about 20 mbar below the reading of my wall mounted barometer.

If I adjust the barometer in the SEA function then the altitude resets to 0 meters.

Also sometimes when I try to adjust these settings it will flash up 'def' and that seems to limit the amount of adjustment.

I have checked the manual twice and can see nothing on def.

Did note though the late warning in the manual about how you could accidentally adjust the calibration when setting units you want measurements in, mbar etc and wondered if I have done this...

Any one else have any similar experiences or can suggest anything?

5:36 a.m. on May 23, 2002 (EDT)
(Guest)

You just may have messed with the caliberation by accident. Give Suunto a call, they may be able to help you. As far as your house moving up and down is concerned, the altitude is measured using barometric pressure, which changes constantly. When using it out in the field make sure you reset the altitude when you are at a known elevation, every now and then. Do not rely 100% on the watch. When used in conjunction with your map it can be a very valuable tool. Just be aware of the change in altitude reading as the weather changes. Also, when you are ascending / descending, the barometer will change as the altitude changes. yada yada yada...read the manual dammit!

Quote:

My old watch died and bought Xlander as a treat to myself.

We live only 650 meters above sea level but I find everynight my house can move upto 100 meters up or down which concerns me.

If I manually adjust the height then the barometer is about 20 mbar below the reading of my wall mounted barometer.

If I adjust the barometer in the SEA function then the altitude resets to 0 meters.

Also sometimes when I try to adjust these settings it will flash up 'def' and that seems to limit the amount of adjustment.

I have checked the manual twice and can see nothing on def.

Did note though the late warning in the manual about how you could accidentally adjust the calibration when setting units you want measurements in, mbar etc and wondered if I have done this...

Any one else have any similar experiences or can suggest anything?

1:37 p.m. on May 23, 2002 (EDT)
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Suunto Altimeters

Quote:

We live only 650 meters above sea level but I find everynight my house can move upto 100 meters up or down which concerns me.

>>> This is within the normal range of daily variation for a pressure (barometric) altimeter. 100 meters of altitude is about 0.33 in.Hg or 11 hPa (by the way, the preferred name for the unit is hectoPascals, the old "millibars" having been replaced a number of years back to honor Pascal, who did a lot of the original studies of pressure). In a given location, the 24 hour variation is often in the 5 to 15 hPa range. Sitting in a given location, your indicated altitude will vary daily and longer term according to weather changes (that's why you can use a barometric altimeter as a weather indicator!).

Quote:

If I manually adjust the height then the barometer is about 20 mbar below the reading of my wall mounted barometer.

>>> Both your wall-mounted barometer and your Suunto need to be calibrated for your location to show the equivalent "reduced" sea level barometer reading. A 20 hPa difference between units is pretty common, even when calibrated at some point in time. Another thing is that the gear train in your wall-mounted barometer (assuming it is an aneroid unit) has a bit of gear lash and hysteresis. Since electronic altimeters have a pressure transducer (mechanical pressure to electric signal converter), there is hysteresis for these units as well (an increase in hysteresis, evidenced by increased lag in indicating altitude change, is an indicator that it is time for a battery change, by the way). Before you recalibrate either one, check (and record) the readings vs the barometer reading from your local airport or weather bureau for a period of at least a week, preferably through a significant weather change. Keep in mind that the airport reports are updated only about once an hour (more frequently if there is significant weather in the vicinity), and the weather bureau potentially even longer between updates. You get the reports via the airport's ATIS (radio or telephone) Try to get the readings within 10 minutes of the new report. Also, you should really be within a couple miles/kilometers of the reporting station for best accuracy.

>>>Another consideration is that the Suunto watches only display in steps of 0.05 inches or 1 hPa. This is pretty coarse. The display is more precise in the calibration mode.

Quote:

If I adjust the barometer in the SEA function then the altitude resets to 0 meters.

>>> This sounds a bit strange. The SEA window (QNH in technical terms, sometimes called the "reduced pressure") should match the local airport value in barometer setting (they will call it "altimeter" setting), if your altitude matches an accurate survey (use government-generated topographic maps). I suspect that you are getting the QFE pressure reading (absolute pressure). In a number of countries, the QFE reading is used to have the altimeter show an altitude of 0 when sitting on the runway. You will have to check your country's flight regulations to determine this. In North America, the QNH reading is used for flights below FL180, and you get the airport altitude from flight charts (above FL180, the standard 29.92 in.Hg/760 mmHg/1013.25hPa is used).

>>> Having said that, there is a peculiarity of Suuntos that affects the SEA display as you go up in altitude. However, at 650 m/2130 ft, you would not see the problem. And the problem is not like you describe.

Try the following: set your known altitude in the altitude window. Go to the first pressure window. Record the pressure shown there. This is the QFE value, the absolute pressure. Multiply your known altitude in meters by 0.1141 and add the result to the absolute pressure. Now step to the SEA window. The value you got should match the SEA window pretty closely. For example, at your 650 m, you get 74 hPa. On a "standard" day, the absolute pressure should be about 940 hPa, giving a SEA (QNH) reading of 1014 hPa. If your local airport is at your same altitude and is giving 940 hPa, they are supplying the QFE (absolute) reading, not the "reduced" equivalent sea-level reading.

>>> For those in "English" unit countries (like the US), there are equivalent calculations, but virtually all those countries give the QNH value as the airport altimeter reading or weather bureau barometer reading.

Quote:

Also sometimes when I try to adjust these settings it will flash up 'def' and that seems to limit the amount of adjustment.

>>> "DEF" = "default". Just release the button, then press it again to continue the setting.

Quote:

I have checked the manual twice and can see nothing on def.

Did note though the late warning in the manual about how you could accidentally adjust the calibration when setting units you want measurements in, mbar etc and wondered if I have done this...

>>> Actually, it is pretty hard to accidentally reset the calibration. There is a "secret handshake" to get into the re-calibrate mode, namely being in the right window and holding a combination of buttons down for a specific length of time. It isn't really that hard to do the recalibration, once you know the procedure. I do it every time I change the battery (a major complaint I have about the Suuntos - if you use the logging and compass functions a lot, battery life is considerably shortened - typically 6 months for my usage pattern). But before you do a recalibration, be sure you understand the discussion I gave above very thoroughly. Particularly, understand the differences among QFE and QNH, the relationship between pressure and altitude, how they relate to the displays on altimeters and barometers, and exactly what data you are getting from your local airport and weather bureau (is it QFE, QNH, absolute pressure, reduced sea-level equivalent, or what?). Then follow the ancient carpenter's rule - measure twice, cut once, and measure again. In terms of your Suunto, this means read the directions completely and thoroughly twice, do a small adjustment, then check the result and think about whether it is in the right direction by the expected amount.

>>> No, it isn't simple. But in reality, it sounds to me like you do not have a problem with the Suunto. You might have a misunderstanding of the meaning of the pressure reading of your wall barometer and what your local airport gives you and might be setting the wrong value into the SEA window. But I doubt, from your description, if there is a problem with the XLander.

9:54 p.m. on December 18, 2002 (EST)
(Guest)

Quote:

My old watch died and bought Xlander as a treat to myself.

We live only 650 meters above sea level but I find everynight my house can move upto 100 meters up or down which concerns me.

If I manually adjust the height then the barometer is about 20 mbar below the reading of my wall mounted barometer.

If I adjust the barometer in the SEA function then the altitude resets to 0 meters.

Also sometimes when I try to adjust these settings it will flash up 'def' and that seems to limit the amount of adjustment.

I have checked the manual twice and can see nothing on def.

Did note though the late warning in the manual about how you could accidentally adjust the calibration when setting units you want measurements in, mbar etc and wondered if I have done this...

Any one else have any similar experiences or can suggest anything?

9:55 p.m. on December 18, 2002 (EST)
(Guest)

Quote:

My old watch died and bought Xlander as a treat to myself.

We live only 650 meters above sea level but I find everynight my house can move upto 100 meters up or down which concerns me.

If I manually adjust the height then the barometer is about 20 mbar below the reading of my wall mounted barometer.

If I adjust the barometer in the SEA function then the altitude resets to 0 meters.

Also sometimes when I try to adjust these settings it will flash up 'def' and that seems to limit the amount of adjustment.

I have checked the manual twice and can see nothing on def.

Did note though the late warning in the manual about how you could accidentally adjust the calibration when setting units you want measurements in, mbar etc and wondered if I have done this...

Any one else have any similar experiences or can suggest anything?

I have experienced the same problem, has anyone been able to help?

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