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I have a Kestrel but I really prefer my mechanical barometer and a small thermometer. I have an older Silva that works great. Silva still makes a mechanical unit. After that, I run DA charts. No batteries. The wind function I find pretty useless. Experience is a better solution for wind.
Silva ADC Ridge Mechanical Altimeter
Density altitude is the altitude relative to the standard atmosphere conditions (International Standard Atmosphere) at which the air density would be equal to the indicated air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. "Density Altitude" is the pressure altitude adjusted for non-standard temperature
Both an increase in temperature, pressure, and, to a much lesser degree, humidity will cause an increase in density altitude. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
Papa Zero Three: Quick question. Why in the standard pressure run are you using a temp of 41.2F and in corrected pressure the temp is 80.0F?
Indespensible for guys that dont really want to learn how to shoot.
I dont know HOW we EVER hit a target in the 'old days' before Kestrels, ballistic computers and scopes that tell us where to aim. It was crazy! Spray and pray! We actually carried PAPER! With NUMBERS on it! Nuts I tell you, NUTS!
I used 80 temp and 80 humidity on the input page but what you see on the Stadard screen grab is what JBM adjusted it to.
OK, then you should check the box for corrected pressure, and change the pressure to 29.92, same temp and humidity. And compare the results.
Corrected pressure is corrected to sea level and standard pressure is 29.92.
[forehead slap] I feel like I am eating crazy pills[/forehead slap] PLEASE, PLEASE, go back and READ what I wrote and READ the screen grab JBM charts from TOP to BOTTOM. I did exactly what you just said and the results are found in the screen grab posted for CORRECTED pressure. Guess what? The firing solutions ARE NOT .1mil difference, it's all explained and plain to see, even with pictures , above.
If after you go back and READ and LOOK at the charts posted and if it still isn't apparent to you, please follow LowLights advice in post #66
It looks like you clicked the Std. Atmosphere box which overrides the conditions you enter, like it does when you choose a bullet versus entering the dimensions manually. That's where the discrepancy is coming from.
I can see everyone's position here... Pinecone is saying if you don't have a Kestrel you can get it near enough with just a map and a thermometer, and LL is saying that a Kestrel will give you more accurate data without having to infer anything.
The way I see it, can you get by without a Kestrel? Of course. But they are cheap and it eliminates one source of error, so why not use one?
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If I put it in just like he says, I get the .1mil difference (9.9 vs 10.0). The only thing that changes is with 29.92 the "pressure is corrected" box is checked and at 24.92 it isn't. Not saying that's correct, just that's how he got it. I don't really get what that proves though. It's just doing the correction for altitude sloppily by yourself vs. letting JBM do it when you can get the exact pressure to begin with from a Kestrel and not have to use an average, guess, or estimate for anything. I also don't get what that had to do with this discussion. If anything it proves that a Kestrel ISN'T a waste (which is what the thread asked about). I don't see why one would argue that using an average and a "close enough" altitude to work backwards is BETTER than a Kestrel. To paraphrase LL, doing it like that may work, but it's ass backwards.I ran every possible scenario I could think of to include intentionally doing it wrong to try and replicate a .1mil difference in firing solutions. The point of the entire exercise being that no matter how you do it, right or wrong,there is no way to get a .1 mil difference in firing solutions as was stated with the given parameters/circumstances.
If I put it in just like he says, I get the .1mil difference (9.9 vs 10.0). The only thing that changes is with 29.92 the "pressure is corrected" box is checked and at 24.92 it isn't. Not saying that's correct, just that's how he got it. I don't really get what that proves though. It's just doing the correction for altitude sloppily by yourself vs. letting JBM do it when you can get the exact pressure to begin with from a Kestrel and not have to use an average, guess, or estimate for anything. I also don't get what that had to do with this discussion. If anything it proves that a Kestrel ISN'T a waste (which is what the thread asked about). I don't see why one would argue that using an average and a "close enough" altitude to work backwards is BETTER than a Kestrel. To paraphrase LL, doing it like that may work, but it's ass backwards.
Here is something you might understand...
At Rifles Only which is 78ft above sea level, in one day we saw a swing in Density Altitude from 3000ft above sea to -2000 ft below sea level. (5000ft) That was in a 24 hour period. No altitude change, but a combination of a front with a drop in temperature. Pressure & Temperature.
If a shooter uses a Kestrel... in order to accurately read Density Altitude you have to use STATION PRESSURE. (This is uncorrected) Station pressure goes below the recorded barometric pressure (corrected)
We are shooting NOT READING THE WEATHER ON TV so we want information that useful to us, without having to carry both a tool for altitude (GPS) and a tool for reading the conditions, a Kestrel. We choose to use a Kestrel so you want to maximize that tool and that information. Density Altitude is a great single number as noted several times including your Dan Thread. DA readings can be taken directly from the Kestrel however you have to set to 0 reference altitude and 29.92 which gives the uses STATION PRESSURE. Not corrected barometric pressure.
See the picture I posted, Denver is 24.92 (roughly) yet one hour from my house I can show as low as 18" ... using that number plus temp I can successfully use a ballistic computer and shoot. I have done this including zeroing a rifle in CO, and traveling to OR with a 4000ft change in altitude. However I did not use Altitude and still was 100% successful.
[forehead slap] I feel like I am eating crazy pills[/forehead slap] PLEASE, PLEASE, go back and READ what I wrote and READ the screen grab JBM charts from TOP to BOTTOM. I did exactly what you just said and the results are found in the screen grab posted for CORRECTED pressure. Guess what? The firing solutions ARE NOT .1mil difference, it's all explained and plain to see, even with pictures , above.
If after you go back and READ and LOOK at the charts posted and if it still isn't apparent to you, please follow LowLights advice in post #66
EDIT: I just know I will probably regret bringing this up but what the hell. GPS derived altitude readings can be quiet a bit off from actual altitude. You mentioned a 3m +/- accuracy which is a best case scenario and is for a physical point on the ground. If your GPS doesn't have a built in barometric altimeter, the GPS uses stored historical data which very likely isn't an exact measurement of the altitude you are at, its an approximation. And even if your GPS does have a built in Barometric altimeter, you need to adjust it like the kestrel if it allows you to, or know if it averages actual altitude data with GPS stored altitude data. I don't want this to turn into a GPS discussion but your thinking that you can use a GPS derived altitude and that it is 100% more accurate than an actual altimeter reading is also erroneous. Here is an article that illustrates how much this can vary and why. GPS and altitude for hang gliding and paragliding | Paragliding : Hang Gliding : Cross Country Magazine
If I put it in just like he says, I get the .1mil difference (9.9 vs 10.0). The only thing that changes is with 29.92 the "pressure is corrected" box is checked and at 24.92 it isn't. Not saying that's correct, just that's how he got it. I don't really get what that proves though. It's just doing the correction for altitude sloppily by yourself vs. letting JBM do it when you can get the exact pressure to begin with from a Kestrel and not have to use an average, guess, or estimate for anything. I also don't get what that had to do with this discussion. If anything it proves that a Kestrel ISN'T a waste (which is what the thread asked about). I don't see why one would argue that using an average and a "close enough" altitude to work backwards is BETTER than a Kestrel. To paraphrase LL, doing it like that may work, but it's ass backwards.
But the BIG ISSUE isn't weather pressure - it's TEMPERATURE!!!
Thanks for the explanation Lowlight. I have been adjusting my altitude on my 4500 AB based off my gps elevation wherever I was shooting and thinking I needed to do it to get the correct dope not realizing I was doing extra steps that we're not needed. I just finished setting my station pressure to 29.92 and not going to mess with it or the altitude again. It will make things much easier when I go to a new area/comp to shoot not having to worry about "adjusting" things to get the right dope
Doesn't GPS base altitude off a sphere? So it wouldn't give accurate altitude anyway. Or do modern device correct for it using the latitude? Sorry I know this isn't a 'How GPS Works' thread.
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So guys...help me out....
There is no doubt you all are more experienced at this then I ever will be but I would like to step into the electronic world for my long range shooting. My problem is that I am not a gadget person at all and small screens & buttons are more work than fun to me but as long as the path (program) is user friendly, I'm good. I have to travel to shoot long and with ammo being what it is "grabbing a case and going shooting" is not a great option.
Kestral products are not inexpensive and I'm not sure what device I need to connect to with the bluetooth option. I have an Iphone but am confused about if it can do what I need or not. I know it has ballistic apps but not sure where to get the "on location" environmental data. Seems like kind of a pain to go to all these different sites for data and try to get it all entered in correctly.
Can you make an economical recommendation on what basic set-up to buy?
The cheapest route is to measure temperature and pressure directly with a thermometer and altimeter. You can guess at humidity because it doesn't matter much. Then plug it all into a $5 ballistics app (take your pick - there are several good ones) on your phone. That will save you a few bucks over a kestrel and do the job pretty much just as well, albeit without the bells and whistles.
We have already acknowledged there is more than one way to skin the cat, been noted, more than once.
You way limits you and sets the kestrel up incorrectly as well the average joe is not going to buy a surveying GPS to align themselves with your way of thinking.
Also going from CO to OR was only a 4000ft change with no difference in temperature and moved the dope from 6.5 to 7.2. Using Station Pressure in a kestrel with AB it was dead on. One unit, no GPS and set up correctly for shooting. That is the key.
Setting it it up correctly for shooting, as it's been acknowledged there are several paths to the same solution but only 1 path gives you 2 answers with a single device, the smaller and lighter kestrel vs your "better", chosen way.
You're so married to your idea you'll defend this poor, inefficient method tooth and nail.
Going from 5000 to 9000 feet here in CO can change the DA from 8,000 to 12,000 even in fall, it's more than one thing, it's more than temp, as noted at Rifles Only, it's a combination, it's generally cooler higher up. Station Pressure accounts for more than one thing with a single number. Like DA does, so why use. Your method that needs a minimum of 4 values especially if you travel. You can't just cherry pick unless you stick to one location. It's a total of several conditions.
Actually I found your pressure swing to go .2 mils either way, .1 from center. That is 1 minute, now combine that 1 minute with other changes that follow like temp. Heck even the .4" of humidity now starts adding up. So your starting to stack errors in a game where we want to shave them.
Like I noted, use your way, but don't try selling it as better, it's a way, just not a very good way for the precision rifle shooter.
I have found this thread to be very useful. The OP asked the very question that has been going through my mind for some time and I am going to see if I can find a Hide vendor that can get me where I want to go. A Kestrel would be fine but going to explore the lower cost options as well. If it gets close to a Kestrel in price or I find a good deal on one, I'll have what I need.
Been doing a lot of looking around, the 4500NV is a pretty nice piece of kit.