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calibrating kestrel 4000- need some help

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Unread 11-09-2007, 08:02 PM
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Join Date: Oct 2006
Posts: 43
calibrating kestrel 4000- need some help

so i received my kestrel 4000 in olive drab. after going through the manual which seems printed in achronological order i found the page for altitude measurment.
since altitude is the height from sea level i drove by the seaside and set the altitude in the Baro screen to '0'. then took the Pressure reading from the Baro screen and inserted it as a reference point in the Altitude screen as dictated by the manual

I then drove to another beach near the sea and wanted to check my altitude which in theory should be '0' too. i did expect some deviation since it says +/- 50feet accuracy but i got a reading of -75ft. is this normal? can this effect readings entered in the PDA ballistic software?

thank you
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Unread 11-10-2007, 05:22 PM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 8,871
To keep the response short, I'd consider using the wind speed and forgetting about barometric pressure. It doesn't make "that" much difference. (in my opinion).

Another thing you could do is to check your readings against a weather station(s) in your area. Google on weather for your location.
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
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Unread 11-12-2007, 03:28 PM
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Join Date: Mar 2006
Posts: 180
When setting these references, I generally go back and forth once or twice to get them to agree, but, IIRC Kestrel says that major changes in baro will require re-calibration, which is why the calibration feature is user-accessible.

I have the same machine, and, FWIW, I don't use these parameters for shooting at all. I just cut to the chase and save myself trying to combine the three most influential environmental factors into the "air density" I'm really after. I use "density altitude", which is independent of any user-calibrations and will be correct whether you set your baro/physical altitude or not.

When using local weather, it is important to know whether you're seeing "station pressure" or pressure corrected for "standard conditions" . . . too much for me.

I use density altitude for running exterior ballistics (and leave all other ballistic computer parameters at "standard metro"), local temp for ammo performance and wind speed for calculating drift. . . .

The beatings will continue until morale improves.
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Unread 11-15-2007, 09:30 PM
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Join Date: Apr 2003
Location: North Bend, Oregon
Posts: 1,524
Oh my, I don't think that is anywhere near optimum. I use station pressure which on your Kestrel set you altitude on the baro screen to zero. Then just use the baro reading. That is station pressure. That is what I put into Exball. Leave the altitude in Exball set to zero. I also plug in the temp and humidity. When I get to where I'm going the first thing I do is set my Kestrel out on a stump or hang on a limb for at least 10 minutes to aclimate.

The altitude readings will not be accurate unless you set your calibration at a known altitude from mean sea level. I live near the ocean and parked within 8' of the water our airports elevation is 17'. My house is at 53' according to Google Earth. Once you set your known altitude in the baro screen you then take that baro reading to the elevation screen and plug it in. At that point you are calibrated for your area. The trouble with this is the baro is rarely perfectly stable. In a short time frame the altimeter will read pretty good but you need to check in periododically at known altitudes to reset the Baro altimeter height and then move the new baro reading to the altimeter screen to get it to match up. It you took it on a week long hike on a dry lake bed at an unknown elevation and you never had a reference point your elevations would vary by hundreds of feet.

Air density is good for tuning internal cumbustion engines. On a given day my Air density altitude will go from -2000' to 5,000' feet. Air density is a calulation based on barometric pressure, air temperature and humidity. If the Kestrel temp moves 10 degrees due to body or vehicle heat or the humidity is off due to being next to your body or in a vehicle or even in it's case it will throw the Air density altitude off hundreds to thousands of feet. Many ways to go wrong with Air Density Altitude. Exball is not calibrated for this anyway so I stick to the station pressure method.

There is a sticky on this topic here. Altitude vs. Barometric pressure
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Last edited by Hired Gun; 11-15-2007 at 09:46 PM. Reason: added the link.
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