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Kestrel's Barometric pressure, do you need to "true" it each day of use?

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Ring

Rifle Instructor
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Minuteman
Dec 12, 2009
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Medina, Ohio
sites.google.com
4500
http://www.nkhome.com/pdfs/kestrel-instructions/K4500_Instructions_7.28.10_WEB.pdf

page 15-16

Barometric pressure is station pressure corrected to sea level. In order to make the correction, the Kestrel
Meter needs an accurate reference altitude. Altitude is the height above sea level. In order to correctly
calculate altitude, the unit needs an accurate barometric pressure reference, also known as an “altimeter
setting”. Fortunately, you only need to know ONE of these values (current barometric pressure or current
altitude) in order to set your Kestrel Meter up to show accurate readings.


so to make sure my DA is right, do i need to set the reference setting mode alt. to my GPS alt?
 
No you want station pressure...

Reference altitude to 0
Reference pressure to 29.92

dont not change it from factory settings then (otherwise) you get corrected barometric pressure. That is not what you want.

The kestrel is not a GPS you want it for the pressure values.
 
It's pretty simple, leave it to factory settings and don't change anything.

Reference Altitude to 0 that is in the Pressure screen

And Reference Pressure to 29.92 in the Altitude Screen

Those are the two you can change and what changes the values we are most concerned with.

This gives you Station Pressure and the Correct Density Altitude.

Do not set it to you location.
 
I posed this question to Nick Vitalbo who wrote the software for the 4500 AB and his reply follows:

"I looked at the code this morning and I ALWAYS pull station pressure for the ballistics computations. I verified that too with the unit as well. So, no matter what you set your altitude reference to on the Applied Ballistics units, it will pull the correct information from the sensors at all times.

Internal to the solver, the only thing that really matters is the air density and it uses the temp/pressure/humidity to compute the air density. The pressure has to be the station pressure or the absolute pressure as measured by the sensor. The barometric pressure is the station pressure corrected for the altitude.

All that being said, if you set your actual altitude on the unit, the only thing it will give you is an accurate barometric pressure, as determined by the station pressure reading from the unit. The ballistics core is always pulling the right numbers internally no matter what you set your altitude to.

This doesn't apply for all ballistics solvers out there though and many of them ask you whether it is station pressure or barometric pressure. The main difference is that barometric pressure is simply corrected for the altitude (what you set as your reference).

Hope that answers it. This is often a point of confusion and I haven't seen too many great online resources to help people understand the difference between them.

Let me know if that clears it up.

Nick

Nick Vitalbo
nVisti, LLC
412-254-4668
[email protected]"
 
yes correct, the DA value from the kestrel is independent of what you set, so to take the number you can disregard either station pressure value or barometric pressure.

but if you need to input these values in a PDA you have to use the correct numbers, to have station pressure put zero in the ref alt, in the baro screen or put the the correct value if you know it for the correct altitude to have the barometric pressure.

at sea level is easy because the reference altitude is always zero.
 
This is interesting and confusing.

I have a Kestrel 3500nv. No ballistic computing built in.
My altitude is 1623m above see level. I am looking for the pressure that i need to insert on online ballistic calculators like JBM and others. I know JBM has an input for altitude.

Now the question. Do i set altitude to sea level or my current altitude?


Sent from my iPad using Tapatalk
 
Blublister said:
This is interesting and confusing.

I have a Kestrel 3500nv. No ballistic computing built in.
My altitude is 1623m above see level. I am looking for the pressure that i need to insert on online ballistic calculators like JBM and others. I know JBM has an input for altitude.

Now the question. Do i set altitude to sea level or my current altitude?


Sent from my iPad using Tapatalk
Click to expand...

Depends which pressure you are working with. Determine that. I prefer to set altitude to zero and put in the proper pressure. Less data to enter.
 
Thanks Shibby.

I will search google a bit and make sure which one is needed for JBM. (Corected or non corected) as i am sure it would make a big difference. From 24.9 inHg to 30.1 inHg.
The 24.9 is what my kestrel gives more or less depending on the day with reference alt set to zerro. The 30.1 is what it gives with my actual altitude (1623m) entered as the refference.

I went on wheather sites to check which pressure they used and most displayed the 30.1 and some displayed the 24.9. This is why i still dont know which one to enter for drop charts and supersonic range.

Thanks for the help


Sent from my iPad using Tapatalk
 
My understanding is that all this confusion arises because of weathermen at different altitudes wanting to be able to compare notes on baro changes that are predictive of weather patterns. So they want to reference/correct everything to sea level. After they do that, if the pressure drops implying some sort of storm front, they can all compare notes with the same reference pressure. "In Denver, the baro is reading 28.4 and the whatever storm is rolling in." That pressure could be understood by the weatherman in Baltimore. He doesn't need to know the altitude in Denver or Albuquerque or wherever - the pressure is referenced to sea level and he knows what it means for meteorological conditions.

For us shooters, we want the actual pressure measured at our location. The units extrapolate altitude from that. And the pressure is what affects flight, not altitude, so I think it's best to just always go by pressure. On Shooter and Ballistic AE, you check the box for "Pressure is Absolute" and put in the station pressure from the Kestrel (mine is 3500). When you do that, the program ignores whatever is put in there for altitude.

And as to the OP - yes, you should measure pressure every day even when you're shooting at the same location. Because of weather pattern changes noted above, your pressure at a given location will vary with meteorological conditions.
 
Last edited:
Blublister said:
This is interesting and confusing.

I have a Kestrel 3500nv. No ballistic computing built in.
My altitude is 1623m above see level. I am looking for the pressure that i need to insert on online ballistic calculators like JBM and others. I know JBM has an input for altitude.

Now the question. Do i set altitude to sea level or my current altitude?


Sent from my iPad using Tapatalk
Click to expand...

It's not interesting at all and was answered...

You can use corrected Barometric Pressure or Station Pressure in JBM, as noted, you should leave it to factory settings and not change it for your location.

JBM can use both, but why would you ... this has been answered and isn't confusing at all.
 
Lowlight said:
It's not interesting at all and was answered...

You can use corrected Barometric Pressure or Station Pressure in JBM, as noted, you should leave it to factory settings and not change it for your location.

JBM can use both, but why would you ... this has been answered and isn't confusing at all.
Click to expand...

Sorry if I offended anyone. I found it interesting because i did not now which one to use or what the difference was between corrected or non corrected pressure.

I now know that i should leave my Kestrel set to zerro. (Change it back to zerro) as was stated.
I found it confusing as I really did not know which one to enter into JBM. I now know after Lowlite replied that i can use both. I did not know what the pressure is corrected tick box meant until i saw this thread. JBM ignores altitude entered unless the "pressure corected" box or "use standard conditions at this altitude" box is ticked. That is why it was interesting for me and I was confused. I was not trying to be deliberately thick.

Thanks to everyone that helped me answer my question.

I now know I have been using my Kestrel and JBM wrong. I was using kestrel on current altitude and not checking pressure is corrected box on JBM. Which means all my drop charts are wrong.

Thanks again


Sent from my iPad using Tapatalk
 
secondofangle said:
My understanding is that all this confusion arises because of weathermen at different altitudes wanting to be able to compare notes on baro changes that are predictive of weather patterns. So they want to reference/correct everything to sea level. After they do that, if the pressure drops implying some sort of storm front, they can all compare notes with the same reference pressure. "In Denver, the baro is reading 28.4 and the whatever storm is rolling in." That pressure could be understood by the weatherman in Baltimore. He doesn't need to know the altitude in Denver or Albuquerque or wherever - the pressure is referenced to sea level and he knows what it means for meteorological conditions.

For us shooters, we want the actual pressure measured at our location. The units extrapolate altitude from that. And the pressure is what affects flight, not altitude, so I think it's best to just always go by pressure. On Shooter and Ballistic AE, you check the box for "Pressure is Absolute" and put in the station pressure from the Kestrel (mine is 3500). When you do that, the program ignores whatever is put in there for altitude.

And as to the OP - yes, you should measure pressure every day even when you're shooting at the same location. Because of weather pattern changes noted above, your pressure at a given location will vary with meteorological conditions.
Click to expand...

How is Shooter combined with the 3500 working out for you? I've been thinking of going this route.

Sent from my SM-N900V using Tapatalk
 
It had us spot on with a DTA HTI in 375 CT and an Armalite AR-50 even with some educated guessing about velocities. In fact, this young lady hit the 825 yard gong on the first shot in a 15 MPH wind with 5 MOA wind dialed in with American Eagle 660 grain ball. Two shots later she whacked this buck at 1100 with the same rifle. I'm a fan.
 

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secondofangle said:
It had us spot on with a DTA HTI in 375 CT and an Armalite AR-50 even with some educated guessing about velocities. In fact, this young lady hit the 825 yard gong on the first shot in a 15 MPH wind with 5 MOA wind dialed in with American Eagle 660 grain ball. Two shots later she whacked this buck at 1100 with the same rifle. I'm a fan.
Click to expand...

That's good. Reason I'm asking, is because I'm between the Kestrel 3500 and 4000. The 4000 does density altitude, the 3500 doesn't. Not sure if that is required, or just an advantage.

Sent from my SM-N900V using Tapatalk
 
OK, now you're over my head. What's "density altitude"? I just recently switched to using baro pressure instead of altitude, and the results were very good. We would go to our shooting location, I'd check the pressure, enter into shooter, and we were off and running. IMHO, shooter is better than ballistic AE because it automatically saves your last inputs as default. That made us way less messed up especially running multiple shooting platforms from the same program. I thought it was a GREAT combo. But perhaps the 4000 would be even better?
 
secondofangle said:
OK, now you're over my head. What's "density altitude"? I just recently switched to using baro pressure instead of altitude, and the results were very good. We would go to our shooting location, I'd check the pressure, enter into shooter, and we were off and running. IMHO, shooter is better than ballistic AE because it automatically saves your last inputs as default. That made us way less messed up especially running multiple shooting platforms from the same program. I thought it was a GREAT combo. But perhaps the 4000 would be even better?
Click to expand...

Density altitude is an option in shooter.

Sent from my SM-N900V using Tapatalk
 
density altitude is a value, absolute pressure + temperature ( humidity is non included in standard scale but has a little influence )

at sea level with the standard value of 15 C ( 59F ) and 1013.2 mb ( 29.92 inhg ) you have a density altitude of 0 meters

when pressure or temperature have different value from standard you can have different density altitude

changing only the temperature, < 15 C you can have negative DA, >15 you can have DA > 0

this for every altitude..
 
one shot ST said:
density altitude is a value, absolute pressure + temperature ( humidity is non included in standard scale but has a little influence )

at sea level with the standard value of 15 C ( 59F ) and 1013.2 mb ( 29.92 inhg ) you have a density altitude of 0 meters

when pressure or temperature have different value from standard you can have different density altitude

changing only the temperature, < 15 C you can have negative DA, >15 you can have DA > 0

this for every altitude..
Click to expand...

Thanks!

Sent from my SM-N900V using Tapatalk
 
Well after messing with mine for several months I reckon I need to send it back to Kestral to have all the factory settings put back in................ I can't find the reset button LOLLOL.
 
I have read the answers here a couple times...maybe I am too stupid to understand. Could someone explain why I should not imput my altitude into my kestrel? As I understand it (admitedly ignorant here) I want the measurement at my current location, right? So why shouldn't I put my current altitude in for it to give me the pressure at my location?
 
If you use Station Pressure, it tells the software where you are... there are several ways to skin the cat, if you correct your barometric pressure for sea level, then you have to use Altitude, if you use Station Pressure it's giving you the actual air density based on your location.

If you use Barometric Pressure (corrected) the Density Altitude will not be correct, if you use Station Pressure (absolute) you have accurate density altitude

This is not confusing and super simple to see, just go to any iPhone Software and change the pressure to "absolute" and it will turn off the ability to even use altitude. If you use altitude and station pressure you are essentially doubling the elevation reading which is why they now gray it out as many people prior to changes were putting in Station Pressure and Altitude then wondering why it was wrong. So they turn it off now.

If you watch in the News in New York City they will tell you that the Barometric Pressure is 29.92, if you then watch the same evening News in Denver they will tell you the Barometric is 29.92... they are correcting it. Denver assumes you know that the elevation is 5280ft above sea level. New York is already there... So by using Station Pressure we are taking the Absolute Values and this is what the software wants. As noted above, or maybe in another thread... even when ballistics software in put inside a Kestrel weather meter it pulls the absolute values and not the corrected... so why use corrected.

if you shoot, and you're smart you record data in the field and not just use software. if you record data, its a good idea to write down the Density Altitude as this one number can be used with no battery solutions like an FDAC. You bullets likes DA as it gives you a single number to where the bullet thinks it is flying. Proper elevation adjustments can be determined with this single value. In order for the DA to be right you need Station Pressure on your meter, hence Altitude is not necessary.

A Kestrel is a PRESSURE METER, pressure is a function of altitude, so if you use station pressure it already assumes the altitude..

I shot on Monday, I had a Station Pressure of 25.25" and a Temp of 31 degrees, my DA was 4000ft, even though I was shooting at 5300ft above sea level. Shooting at the same range in the summer my DA is 8000ft. What that translates to is, in the summer i use less dope, and in the winter more dope. Higher DA means happier bullet, lower Station Pressure means Happier bullet, higher temperatures means Happier Bullet... Humidity is too small to worry about, so skip the humidity and focus on the DA instead.
 
the most of the ballistic software accept absolute pressure or barometric pressure and altitude, the easy way is to use absolute pressure, to have this value in the baro screen in the Alt reference you have to put zero and you have always the absolute pressure, in this manner you can disregard if the pressure is changed due a storm ecc ecc......

but if you know your current altitude you can use this a input, but every time you change altitude or the barometric pressure changes you have to correct the values.

the best way to use density altitude is when you are using back up ( or primary ) ballistic tables with the DA parameter, in this case a kestrel 4000/4500 gives you a DA, you check the DA and use the correct table.

if you use another kestrel you have to bring absolute pressure and temperature to interpolate and find the actual DA, always to use a table.

but if you want to use a PDA with a software and you want to give to it a barometric pressure and your current altitude you can do it..

is not always easy to have the correct altitude ( if you want to be perfect ) because for example you are hunting in the mountains and your path starts at 4000 ft and finished at 11000 ft, with no accurate landmarks to check your current altitude, you can also use a GPS altitude but sometimes you can input some error more..

all these considerations are valid ( for me ) for extreme ELR shooting and with normal skill is possible to have some good outputs
 
opssss I post at the same time of Frank.... may be the same concepts, probably Frank explain better... this is not my language ;-)
 
Thanks for the replies to my questions.

I was not being deliberately thick, but i could not figure it out. I finally got it now. I will set my reference altitude back to zero.
I found this thread interesting because it pointed out my mistakes. I was using the kestrel with reference altitude set to my current location altitude. This value was then inserted into JBM. I did not know what the pressure has been corrected check box was so I did not tick it. According to the JBM website the altitude entered is not considered unless the "standard conditions for altitude" or "pressure has been corrected" check boxes have been ticked.

This means that my drop charts will not be correct?

Do I have this right? If the reference altitude on your Kestrel is set to zero you should tick the pressure has been corrected check box in JBM.
 
JBM has these little question marks to explain things.

Pressure is CorrectedCheck this box if the pressure entered is a corrected station pressure. If it is an absolute pressure, leave this unchecked.

Std Atmosphere at Altitude
When checked, the temperature, pressure and humidity for standard atmospheric conditions at the entered altitude (always 0% at standard conditions) are entered in the calculation. The standard used is the ICAO standard atmosphere.

Pressure
The barometric pressure. It may be corrected or uncorrected depending on the state of the "Corrected Pressure" checkbox.
Click to expand...

so just put in your exact values from the factory settings in your kestrel and you leave the boxes unchecked. The altitude can stay at 0.0. cause you are using Station Pressure (absolute).
 
Thanks Lowlight

Now I am on the same page. Is there a way I can convert station pressure back to absolute pressure?
The reason I am asking is because I have written the station pressure down in my log book every time I went to the range.
If I can convert this back to absolute pressure I will not lose all my dope. I know the exact elevation for the ranges that was used (from Google earth). Or would you say just start fresh?

I know I might be opening a whole new can of worms with this question.
 
Absolute and Station pressure are the same thing... You have corrected Barometric Pressure.

Off the cuff for every 1000 feet of elevation you go up, subtract 1" of pressure.

Example, sea level is 29.92, Denver is at 5000ft so your Station Pressure is 24.92. But that is just a rough estimate.
 
Nether mind, I found this site that has an online converter from station pressure to sea level pressure.
Makes it real quick and simple to convert all previous dope collected in station pressure to absolute pressure.

Here is the link for anyone interested
Station Pressure Calculator

Hope this can help someone
 
I just posted a link to an online converter from station pressure to sea level pressure. It should be up soon as soon as it gets approved by mod.
 
Just so I am clear on this...the bullet doesnt care about the elevation. Just density altitude. Density altitude is absolute pressure at the surface regardless of altitude correct?
 
Yes the bullet cares about the pressure of the air where you are, uncorrected - the absolute pressure that the instrument measures. It could give a damn what the pressure is at sea level or on everest or underneath the ocean or on the moon. That's for the meteorologists. The bullet also cares about temperature. The 2 combined is density altitude.
 
So if I get a reading strait off of the pressure sensor on my fone just plug that in
 
The phone has no pressure sensor. It tries to estimate it using altitude from the GPS. Or it may try to pull the corrected pressure and temp from a weather station (which can be wildly wrong-I frequently see them report uncorrected pressure as corrected).

Sent from my iPad using Tapatalk HD
 
Is sync on or off in the pressure and alt screens. 2nd. When capturing wind reading to go into the firing solution can I just use the 3 o'clock or 9 o'clock reading instead of putting the back into the wind direction? Will that give correct values? If am reading crossways wind is that same as reading full wind then adjusting to firing angle?
Thanks,
T
 
Last edited:
Sorry, I know this is different software, but I have Shooter for Android. If I input the DA and temp from my Kestrel 4000, will this work? What I'm really asking, is this the best way?



Sent from my SM-N900V using Tapatalk
 
nicholas306 said:
Sorry, I know this is different software, but I have Shooter for Android. If I input the DA and temp from my Kestrel 4000, will this work? What I'm really asking, is this the best way?
Click to expand...
You don't want to use the DA if you've got a kestrel to work with. You want the actual station pressure.

You want to go into your Preferences and change from Simple to Advanced first of all.

Then when you get to your atmospheric conditions page...Check the box next to "pressure is absolute"
That will eliminate the "altitude" variable and make your "density altitude" variable change to "station pressure" which is what you want.

Then you can enter in your exact "station pressure" according to your kestrel. Assuming of course that you followed Franks advice and have your Kestrel set correctly.
 
toddconley said:
Is sync on or off in the pressure and alt screens. 2nd. When capturing wind reading to go into the firing solution can I just use the 3 o'clock or 9 o'clock reading instead of putting the back into the wind direction? Will that give correct values? If am reading crossways wind is that same as reading full wind then adjusting to firing angle?
Thanks,
T
Click to expand...

Anybody know the answer to this question?


Sent from my iPhone using Tapatalk
 
Sync question answer. It is up to you whether you want to sync your attitude and barometric pressure. If you know your attitude then baro will be correct when sync is on. The inverse is also correct if you know your baro then your attitude is correct with sync on. On my 4500nv neither of these settings affect density attitude it specifically says this in the instructions. If you want your attitude to relate to your density attitude then set your attitude to 0 ft. Your barometric pressure will then be wrong. This doesn't matter though because you need to choose how you are going to collect data. Either use density attitude or barometric pressure. Unless your super anal and want both but that will require two separate dope cards that will have the similar info. Density attitude is better because your dope cards can be instantly generated with modern shooting software. Your wind questions need refinement. The measurement your taking is at your location you might have 2 or 3 different winds to 1000 and they are constantly changing.
 
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