Easy recalibration of 60csx altimeter

[+greenbriel]

If I go to a local benchmark, calibrate my altimeter, then immediately proceed home and record the indicated altitude, will the recorded altitude be accurate enough to calibrate from next time without having to go to the benchmark again?

 

I imagine it would be best to do this when the barometer trend is pretty flat.

 

Cheers,

 

-G

[+hurley_108]

If I go to a local benchmark, calibrate my altimeter, then immediately proceed home and record the indicated altitude, will the recorded altitude be accurate enough to calibrate from next time without having to go to the benchmark again?

 

I imagine it would be best to do this when the barometer trend is pretty flat.

 

Cheers,

 

-G

 

Probably, particularly if the benchmark is nearby. The alternative is you could leave your GPS somewhere in your yard and let it average for hours and hours. You'll probably get a pretty good altitude that way too.

[Alphawolf]

If I go to a local benchmark, calibrate my altimeter, then immediately proceed home and record the indicated altitude, will the recorded altitude be accurate enough to calibrate from next time without having to go to the benchmark again?

 

I imagine it would be best to do this when the barometer trend is pretty flat.

 

Cheers,

 

-G

 

Yup...That'll work. Or, if you have an airport nearby, call the recording pilots use and get a current barometric pressure and use that to calibrate. Then, immediately read the altitude of your driveway and record it. You can then use the known altitude of your driveway to calibrate against at any time.

[+Snoope]

If you go to a previous posting by me about this subject this is what I do and it works out very well. Post #6 Snoope.

http://forums.Groundspeak.com/GC/index.php...p;#entry2755608

[+Snoope]

I forgot on my previous posting to say that after I got my readings at the airport benchmark, I quickly drove home which is about 3 blocks away, took a reading of the elevation in my driveway and then I set the altimeter to my driveway reading before I go cachng.

[shivia]

I forgot on my previous posting to say that after I got my readings at the airport benchmark, I quickly drove home which is about 3 blocks away, took a reading of the elevation in my driveway and then I set the altimeter to my driveway reading before I go cachng.

- why do you need to approach closely to your nearby airport while you're 3 blocks away? Stay at home and take the barometer pressure value as per the weather report of this airport in the internet: the result is not the same?

- I live about 8 miles straight line from airport. I always take the pressure value from the weather report of this airport in the internet to calibrate my 60csx.

[+greenbriel]

Thanks folks!

 

I hadn't thought of using a nearby airports weather report, that's a great idea. I am a bit less than 10 miles from the closest airport, I guess that's close enough?

[+Mtn Summit]

I have the 60CSx - a dumb question - I would think the GPS unit would not need to be calibrated for altitude, because the GPS coordinate with triangulation, etc.., would be able to pinpoint your location, thus knowing the altitude?

[+greenbriel]

I have the 60CSx - a dumb question - I would think the GPS unit would not need to be calibrated for altitude, because the GPS coordinate with triangulation, etc.., would be able to pinpoint your location, thus knowing the altitude?

 

I'm not sure which of two things you mean here, so here's two answers

 

1) The maps don't contain altitude information. Topo maps have contour lines, but AFAIK, they are merely graphics, no altitude data is actually stored in the map.

 

2) GPS calculated altitude isn't very accurate (I believe generally +/- 50ft, can anyone correct me?), while the 60csx altimeter, when calibrated, is accurate to a couple of feet.

[+Snoope]

Yes, I believe the GPS elevation is not real accurate. If you get the pressure information from your local airport over the Internet , I found out that it is not updated very often. If you have a scanner and you can receive the transmitted over the air information it is updated very frequently so the pilots can set their altimeter. If you are some distance from the airport and you set your GPS elevation with that info it will not be correct because your location elevation will be different from the airport. I think the best way is to find a benchmark desk. Also, remember to make sure the units in the GPS are set to inches or millibars, which ever is necessary in your area. Snoope

[+imajeep]

Can I not read my altitude from a topo map?

[+greenbriel]

Can I not read my altitude from a topo map?

 

Sure, but it wouldn't have good accuracy when between contours, right?

 

I realize we are talking about more detail than you'd probably ever need, but isn't that half the geeky fun of owning a GPS?

[+Mtn Summit]

OK, so if I understand right, I can use my Topo Map, say National Geographic's Topo's, and If I can pinpoint where I will be ahead of time on my computer, I can take a reading from that, and when I get in the field, at that point, calibrate the GPS, and it will now have me within a few feet of accurate elevation?

 

I assume each time I went out, if possible, I would have to calibrate the unit to a known elevation? I guess I still do not understand why multiple satelites cannot pinpoint an exact elevation on the GPS?

[+imajeep]

Sure, but it wouldn't have good accuracy when between contours, right?

 

I realize we are talking about more detail than you'd probably ever need, but isn't that half the geeky fun of owning a GPS?

Good point. I live in Chicago, which is basically a cornfield. So my reaction would be "What contours?"

 

And it's more than half the geeky fun of owning a GPS, at least for me. I posted a question yesterday on how to change the measurement units on my GPS when projecting a waypoint, to eliminate the 26.4-foot maximum error involved in rounding to the nearest hundredth of a mile! Any normal person would think I was nuts! But not here, which is one of the reasons I like it.

[+briansnat]

I have the 60CSx - a dumb question - I would think the GPS unit would not need to be calibrated for altitude, because the GPS coordinate with triangulation, etc.., would be able to pinpoint your location, thus knowing the altitude?

 

I'm not sure which of two things you mean here, so here's two answers

 

1) The maps don't contain altitude information. Topo maps have contour lines, but AFAIK, they are merely graphics, no altitude data is actually stored in the map.

 

2) GPS calculated altitude isn't very accurate (I believe generally +/- 50ft, can anyone correct me?), while the 60csx altimeter, when calibrated, is accurate to a couple of feet.

 

The topo contour lines do have altitude info. To calibrage my 60CSX I walk to a contour line, find out my elevation as stated on the topo map and then make sure my altimeter matches that.

[+DENelson83]

Yup...That'll work. Or, if you have an airport nearby, call the recording pilots use and get a current barometric pressure and use that to calibrate.

If you have a radio scanner, you can easily access that recording, known as ATIS, to get your current altimeter setting. The ATIS where I live is on 118.6 MHz.

[+imajeep]

Yup...That'll work. Or, if you have an airport nearby, call the recording pilots use and get a current barometric pressure and use that to calibrate.

If you have a radio scanner, you can easily access that recording, known as ATIS, to get your current altimeter setting. The ATIS where I live is on 118.6 MHz.

Most of the weather sites post barometric pressure data, too.

[+greenbriel]

Sure, but it wouldn't have good accuracy when between contours, right?

 

I realize we are talking about more detail than you'd probably ever need, but isn't that half the geeky fun of owning a GPS?

Good point. I live in Chicago, which is basically a cornfield. So my reaction would be "What contours?"

 

And it's more than half the geeky fun of owning a GPS, at least for me. I posted a question yesterday on how to change the measurement units on my GPS when projecting a waypoint, to eliminate the 26.4-foot maximum error involved in rounding to the nearest hundredth of a mile! Any normal person would think I was nuts! But not here, which is one of the reasons I like it.

 

I know, I posted in that thread too - looks like we are the same subgroup of geek

[+greenbriel]

The topo contour lines do have altitude info. To calibrage my 60CSX I walk to a contour line, find out my elevation as stated on the topo map and then make sure my altimeter matches that.

 

Well, yes, obviously I understand that each contour line represents a specific altitude, what I meant is that there is no electronic altitude data in the map. i.e. the GPSr has no way of using the fact that you are at a contour line to calibrate the altimeter automagically.

[John E Cache]

I assume each time I went out, if possible, I would have to calibrate the unit to a known elevation? I guess I still do not understand why multiple satelites cannot pinpoint an exact elevation on the GPS?

The GPS gives a 3D fix if you have 4 sats. I think the vertical precision isn't very good. My old GPS didn't have a barometer and the altitude wandered all over the place. See: Dilution of precision (DOP) It looks like the VDOP is the number that gives vertical accuracy. I wonder what a typical VDOP number is.