Using pressure instead of altitude

[MuleyFever]

I downloaded the Leica app to use with the the 3200.com and the app uses pressure (inhg) rather than altitude. It got me thinking. Would using pressure be more accurate? If going off altitude you could be under a high or low pressure system so the air would be different under those conditions.

 

[TNKnoxville]

Probably more accurate but it changes over the course of a day, depending on the weather patterns. Would be interesting to run some numbers and see if there is a significant or useable/practical difference. I'm an engineer and use "hg in many of our work applications.

 

[TNKnoxville]

German engineers like very precise measurements

 

[Jordan Smith]

I downloaded the Leica app to use with the the 3200.com and the app uses pressure (inhg) rather than altitude. It got me thinking. Would using pressure be more accurate? If going off altitude you could be under a high or low pressure system so the air would be different under those conditions.

Yes. Altitude is just a roundabout way to calculate the pressure, which is one of the variables that determines air density, which is the end-goal quantity of interest when it comes to atmospheric influence in aerodynamics.

 

[Formidilosus]

I downloaded the Leica app to use with the the 3200.com and the app uses pressure (inhg) rather than altitude. It got me thinking. Would using pressure be more accurate? If going off altitude you could be under a high or low pressure system so the air would be different under those conditions.

When you say “altitude”, do you mean density altitude?

 

[alexnelon]

Pressure is more accurate and also way easier because pressure is so easy to measure. Even your phone has a barometer in it.

 

[JF_Idaho]

Pressure is more accurate and also way easier because pressure is so easy to measure. Even your phone has a barometer in it.

Most phones and apps only give you barometric pressure. The ballistics app needs station pressure (at least the ones I use), so you need to know your altitude to convert barometric to station anyways.

 

[alexnelon]

Most phones and apps only give you barometric pressure. The ballistics app needs station pressure (at least the ones I use), so you need to know your altitude to convert barometric to station anyways.

Barometric pressure is a function of station pressure corrected for altitude. I'm not aware of a single ballistics app that goes to the trouble of converting the raw station pressure reading from your phone's sensor into barometric pressure just so you can't use it in the app.

 

[AM_Hunter]

Pressure is more accurate and also way easier because pressure is so easy to measure. Even your phone has a barometer in it.

How can you measure pressure on an iphone? Is it a third party app?

 

[alexnelon]

How can you measure pressure on an iphone? Is it a third party app?

The sensor is just built in but ballistic apps use it too. The phone uses it mostly to for fitness apps to keep track of how many flights of stairs you climb. There isn't a default "check my pressure" option in the OS because it isn't really useful for anybody but us.

 

[AM_Hunter]

The sensor is just built in but ballistic apps use it too. The phone uses it mostly to for fitness apps to keep track of how many flights of stairs you climb. There isn't a default "check my pressure" option in the OS because it isn't really useful for anybody but us.

Gotcha, maybe theres some decent apps that can pull it. The weather app shows pressure but not really useful if you dont have reception.

 

[justin davis]

Density Altitude?

 

[MuleyFever]

When you say “altitude”, do you mean density altitude?

I mean altitude in feet. I maybe should have said elevation.

 

[Jordan Smith]

Gotcha, maybe theres some decent apps that can pull it. The weather app shows pressure but not really useful if you dont have reception.

Look for the app "Barometer" in the app store. It works well and reads gauge/station pressure.

 

[Formidilosus]

I mean altitude in feet. I maybe should have said elevation.

What is it that you are trying to do?

 

[MuleyFever]

What is it that you are trying to do?

View attachment 913373

I was just curious about the difference and accuracy, if any, in using pressure over elevation. I have never seen an app that didn't ask for elevation.

 

[BULLBLASTER]

a solver that asks for elevation is just using that to approximate air pressure.

Station pressure drops very close to 1 inHG per 1000 feet elevation starting at roughly 30 inHG at sea level. Weather will cause minor differences though.

 

[JF_Idaho]

Barometric pressure is a function of station pressure corrected for altitude. I'm not aware of a single ballistics app that goes to the trouble of converting the raw station pressure reading from your phone's sensor into barometric pressure just so you can't use it in the app.

I am on android, so iphone might be better. I haven't found a single app that gives me uncorrected/station pressure. Of the 3 ballistic apps I use, Strelok pulls from weather station and gives corrected/barometric pressure, Hornady gives you nothing but an entry, and AB Quantum gives station pressure. Most weather apps give you corrected/barometric pressure.

Looks like the screenshot Form posted shows barometric as well unless he is actually at Sea level.

 

[Shortschaf]

Altitude has zero direct affect on external ballistics

Air density does
Air density changes with pressure, temperature, and (in a really small way) humidity
Pressure can be roughly estimated with altitude

Pressure values given through most weather apps or stations are usually "corrected" which means you must include altitude to undo that correction.

Absolute pressure is the actual pressure and is independent of altitude

Density altitude is a term that combines a standard pressure, standard temp, and standard humidity level at a certain altitude. So air density is able to be summarized into a single, altitude value

 

[mxgsfmdpx]

This is going to sound kind of gay but…

The overall goal is to make the best possible guess at what the air FEELS like for the bullet to fly through in that moment and at that location; in order to obtain a best guess calculation for the ballistics. That’s it.

When my dad was flying airplanes in the 70s they understood the concept even back then and way before then with flying planes through air. Early on they used a form of pressure altitude which is known altitude adjusted for atmospheric pressure. Later, density altitude came along to further refine the overall solution by factoring in temperature as well.

You can land on pretty damn good guesses by simply using elevation and temperature and a simple line graph for “feels like air”. Some of the solvers already have this built in when you manually enter an elevation and temp.

So, some solvers are using a form of pressure altitude, some are using just temperature and altitude and a calc in the backend, and some, with on board sensors or weather data synced from a device gathering closest station pressure, temp, and elevation are coming up with density altitude for the correction.

They all work. And at most hunting range shots with modern bullets, with known/good BCs, especially once data is trued up in the solver, you aren’t missing an animal because you didn’t factor in the weather data perfectly.

It’s still important to have a general idea of feels like air for the bullet which nearly all solvers now a days correct for via different methods.

Run some numbers on, say, a 147 ELDM at 2,800 FPS, at 300 yards. The difference between shooting in Alaska at 0 degrees and 0 feet of elevation and in Arizona in 110 degrees and 5,000 feet is probably only a tenth of a MIL.