Range Report Why so few just using station pressure?

[Grump]

As a kid, I used to wonder how altimeters could be accurate without knowing barometric pressure, because I also knew that barometric pressure was "corrected" to the equivalent sea level values.

Never bought one.

Anyway, my understanding of this sea of air we push bullets through is that the combined effect of altitude and barometric pressure is just the "station pressure", the raw reading of psi or Bar or whatever unit you choose.

One value, one number, and I think a *few* ballistics programs allow that entry as an alternative to altitude and corrected barometric.

So why is this approach not more common? Are we a bunch of VHS users ignoring the BetaMax advantage?

 

[bohem]

Re: Why so few just using station pressure?

I don't have a way to input it directly or I'd do exactly that. When my pockets allow for a Kestrel that has the capability I'll be getting one.

 

[ReaperDriver]

Re: Why so few just using station pressure?

It took me a little while to see the light, because as a pilot - all my mind could comprehend was baro pressure. Now that I have a Suunto watch with absolute or station pressure available at my fingertips (literally) - my ballistic iphone apps have been MUCH more accurate.

I think that's the heart of the problem though.... unless you have the Suunto or Kestrel - there is no good source of station pressure. But what most people have is access to the internet to directly download into the ballistic app - and all you can get there is sea level baro pressure.

 

[jrob300]

Re: Why so few just using station pressure?

I can't afford a Kestrel right now. So my wife and kids just bought me one of these for my birthday:

http://accurateshooter.wordpress.com/2008/06/21/timex-altimeter-barometer-thermometer-watch/

I can't comment on how accurate it is, but it does give sea level and actual pressure. I'm assuming that's the same as station pressure? I think it was $69.00, but I'm not supposed to know that.

John

 

[memilanuk]

Re: Why so few just using station pressure?

Uncorrected or 'raw' pressure is all I use...

 

[ReaperDriver]

Re: Why so few just using station pressure?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body">I can't afford a Kestrel right now. So my wife and kids just bought me one of these for my birthday:

http://accurateshooter.wordpress.com/2008/06/21/timex-altimeter-barometer-thermometer-watch/

I can't comment on how accurate it is, but it does give sea level and actual pressure. I'm assuming that's the same as station pressure? I think it was $69.00, but I'm not supposed to know that.

John </div></div>

I'll bet it works just fine. I don't know how good the Timex is but my Suunto was dead on with the pressure reading from a Friend's Kestrel on the several times we've been at the range together.

And yes Actual pressure = station pressure.

 

[jrob300]

Re: Why so few just using station pressure?

Cool... I'm a cheapskate.

The guys at AccurateShooter seemed OK with it.

I'll check vs. field data in the next week or so.

John

 

[ewoaf]

Re: Why so few just using station pressure?

i use it

 

[azimutha]

Re: Why so few just using station pressure?

There is no practical difference in results between using station pressure vs. corrected pressure + altitude.

The issue really is whether you can get a current measurement for your present location. The advantage of using station pressure in your ballistics calculator is that you can leave the altitude field empty or set @ zero.

I use my Garmin GPS unit's built-in sensor (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1696382) and it is accurate.

 

[Rafael]

Re: Why so few just using station pressure?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body">There is no practical difference in results between using station pressure vs. corrected pressure + altitude.

The issue really is whether you can get a current measurement for your present location. The advantage of using station pressure in your ballistics calculator is that you can leave the altitude field empty or set @ zero.

I use my Garmin GPS unit's built-in sensor (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1696382) and it is accurate. </div></div>

That is the reasoning I use.....one variable instead of two.
Of coure, DA would further reduce variable count....but I do not have a device that gives me DA.

 

[azimutha]

Re: Why so few just using station pressure?

My ballistics calc (iPhone/Touch Ballistic) has an option to use DA, but my understanding is that DA charts are something you use when you don't have a ballistics calculator at your disposal.

 

[Rafael]

Re: Why so few just using station pressure?

Yes sir, it certainly reduces the number of tables you need.

 

[ReaperDriver]

Re: Why so few just using station pressure?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body"><span style="font-weight: bold">There is no practical difference in results between using station pressure vs. corrected pressure + altitude.</span>

The issue really is whether you can get a current measurement for your present location. The advantage of using station pressure in your ballistics calculator is that you can leave the altitude field empty or set @ zero.

</div></div>

I agree with you on the bolded part as long as you're standing on an airfield where you can get an accurate sea level altimeter setting. But I've found significant differences being only 10 miles away and 700' higher than the airfield where I got my current sea level corrected pressure. Especially from 600-1000 yds, the station pressure has been spot on where the corrected pressure data was not matching my observed dope very well.

 

[azimutha]

Re: Why so few just using station pressure?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body"><span style="font-weight: bold">There is no practical difference in results between using station pressure vs. corrected pressure + altitude.</span>

The issue really is whether you can get a current measurement for your present location. The advantage of using station pressure in your ballistics calculator is that you can leave the altitude field empty or set @ zero.

</div></div>

I agree with you on the bolded part as long as you're standing on an airfield where you can get an accurate sea level altimeter setting. But I've found significant differences being only 10 miles away and 700' higher than the airfield where I got my current sea level corrected pressure. Especially from 600-1000 yds, the station pressure has been spot on where the corrected pressure data was not matching my observed dope very well. </div></div>

That brings up some interesting questions. If you refer to my previous post - http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1696382 - I can verify that using my GPS I got accurate readings because I calibrated it at a known altitude and took my readings later at a known altitude. But does that mean I can always count on the GPS unit to be accurate and properly calibrated? I certainly can't always know my altitude for certain.

What I'm wondering is whether its station pressure ("Ambient Pressure" in Garmin-speak) will always be accurate, regardless of whether the unit is calibrated. If so, that would be better than having to worry about remembering to calibrate it. I'll have to perform a test, such as purposely miscalibrating it with the wrong altitude, then set it to use station pressure. I can easily drop by the airport and use their free wi-fi to check their readings.

As already established, using station pressure, if you can get it, is better because you can leave the altitude field always zeroed.

 

[Grump]

Re: Why so few just using station pressure?

I thought that station pressure makes altitude irrelevant.

Just measure the "thickness" of the air and calculate drops and wind from that.

As stated above, one variable instead of two. On the other hand, I've always been okay with known altitude and local-measured temperature, and leaving barometric at "default". It would appear that baro is the smallest portion of the station pressure.