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Station Pressure and Ballistic FTE

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  #1  
Unread 07-12-2010, 11:55 PM
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Station Pressure and Ballistic FTE

I've been reading heavily in regard to the use of station pressure rather than corrected barometric pressure when working a shooting solution. I'm trying to setup Ballistic FTE correctly, but I'm not completely sure of the settings. My hope is that with some help, we can figure it out and people like myself will be able to reference it here via a simple google search. I'll try to explain my understanding, then you guys can maybe tell me where I'm off or shine some light.

To get the station pressure I use my kestrel 4000NV on the barometric pressure page, with a reference altitude set to zero. If I understood correctly, this reading is the station pressure rather than corrected baro. Am I correct on that?

So on to Ballistic. The way I understand station pressure as it relates to most ballistic programs is this: Set the elevation to "0" and put the station pressure into the "baro pressure" field. Am I correct on that?

In the "trajectory" page there is a section for "zero atmosphere" and "current atmosphere." My understanding of this is that zero atmosphere is the exact range conditions when the rifle was zeroed and current is the conditions as they are at the time of the shot you are making now. On both the zero atmosphere and current atmosphere pages there is a setting of "on" or "off" for "Pressure is absolute."

My question is, what exactly does this setting control, and how does it relate to using station pressure?

Thanks in advance!
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  •   #2  
    Unread 07-14-2010, 11:51 AM
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    Re: Station Pressure and Ballistic FTE

    I have been using it with absolute pressure set to "off" and it seems correct. I am the type that likes to "know" rather than "think I know" however.

    Anybody care to take a stab?
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      #3  
    Unread 07-14-2010, 12:14 PM
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    Re: Station Pressure and Ballistic FTE

    I do the same and it is working for my 6.5-284 and my 338 Edge out to 1000 yds. I've played a lot with the settings and then compared with real world results to get them to match up.
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      #4  
    Unread 07-14-2010, 03:57 PM
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    Re: Station Pressure and Ballistic FTE

    I always use station pressure and leave the elevation on zero, works to way beyond 1K
    RR
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      #5  
    Unread 07-14-2010, 04:42 PM
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    Re: Station Pressure and Ballistic FTE

    Quote:
    Originally Posted by Ridge Runner View Post
    I always use station pressure and leave the elevation on zero, works to way beyond 1K
    RR
    Right, I understand that part. What I'm not sure on is the "pressure is absolute: on, off" button in ballistic FTE.
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      #6  
    Unread 07-14-2010, 06:04 PM
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    Re: Station Pressure and Ballistic FTE

    Now you've had me messing with mine for an hour. I may be wrong but I'll take a stab at it. Absolute pressure is station pressure. If you turn on "pressure is absolute" you can on can only enter baro. pressure. Therefore, when you read your Kestral, you have to have altitude referenced to zero so you get a station pressure and then enter that into Ballistic FTE. If you turn off "pressure is absolute", you can enter baro. pressure and altitude. So your Kestral would have to give you an accurate elevation and a corrected pressure reading to enter into Ballistic FTE. I think you're better to leave elevation set to zero on both and use the station pressure reading. If I set elevation to zero and enter station pressure on Ballistic FTE, I can turn "pressure is absolute" on or off and it doesn't effect my trajectory print out untill I change the elevation.
    My recommendation:Use station pressure, turn on "pressure is absolute" then you can't change elevation from zero.
    On or off doesn't matter as long as elevation is set to zero and you enter station pressure.
    I hope this didn't muddy it up too much. Again, I've had to just play with mine until I start figuring it out.
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      #7  
    Unread 07-14-2010, 08:03 PM
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    Re: Station Pressure and Ballistic FTE

    Thank you jumpalot. I can't believe I didn't notice that. You are dead on the money. When I turn "pressure is absolute" on, it gray's out the altitude and doesn't allow you to enter anything.

    ... provided we aren't missing something else that its doing.
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