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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Altitude vs. Barometric pressure
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<blockquote data-quote="Mikecr" data-source="post: 147001" data-attributes="member: 1521"><p>1kft pressure differences under 'standard atmosphere at altitude' conditions might be assumed -.88"hg as rounded. A median value. But this would actually only be correct from 6500'to 7500'. </p><p>Here's an example:</p><p>ICAO --&gt;</p><p>59deg</p><p>29.92126"hg</p><p></p><p>0 to +1000ft=</p><p>29.92" to 28.86" --&gt; -1.06"</p><p></p><p>5000ft to 6000ft=</p><p>24.90 to 23.98 --&gt; -.92"</p><p></p><p>+9000ft to 10,000ft=</p><p>21.39 to 20.58 --&gt; -.81"</p><p></p><p>However, these are just cumulative small errors..</p><p></p><p>The Krestel does give density altitude as calculated based on it's sensed absolute pressure, temp, and humidity. It calculates this rather than measuring it. Therefore, I submit that density altitude is not the most accurate air density parameter to use in ballistics.</p><p>Does pejsa's ballistic program allow density altitude inputs? I don't know..</p><p>According to his user manual, it doesn't appear so:</p><p><a href="http://www.pejsa.com/manualPage2.htm" target="_blank">http://www.pejsa.com/manualPage2.htm</a></p><p></p><p>There is an error in his ascertion regarding air density on page3 that you might want to pass on. Specifically, the part about StdMetro air density being equal to conditions of 39.4deg &amp; 1000ft(This is equal to ICAO +78%rh, rather than StdMetro).</p><p>Small errors...</p></blockquote><p></p>
[QUOTE="Mikecr, post: 147001, member: 1521"] 1kft pressure differences under 'standard atmosphere at altitude' conditions might be assumed -.88"hg as rounded. A median value. But this would actually only be correct from 6500'to 7500'. Here's an example: ICAO --> 59deg 29.92126"hg 0 to +1000ft= 29.92" to 28.86" --> -1.06" 5000ft to 6000ft= 24.90 to 23.98 --> -.92" +9000ft to 10,000ft= 21.39 to 20.58 --> -.81" However, these are just cumulative small errors.. The Krestel does give density altitude as calculated based on it's sensed absolute pressure, temp, and humidity. It calculates this rather than measuring it. Therefore, I submit that density altitude is not the most accurate air density parameter to use in ballistics. Does pejsa's ballistic program allow density altitude inputs? I don't know.. According to his user manual, it doesn't appear so: [url="http://www.pejsa.com/manualPage2.htm"]http://www.pejsa.com/manualPage2.htm[/url] There is an error in his ascertion regarding air density on page3 that you might want to pass on. Specifically, the part about StdMetro air density being equal to conditions of 39.4deg & 1000ft(This is equal to ICAO +78%rh, rather than StdMetro). Small errors... [/QUOTE]
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Altitude vs. Barometric pressure
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