Home Forums Hunting & Shooting Hunting Optics How to use that new SWFA scope- reticle, turrets and proper usage.

You're right about the calculations, though RH does affect a ballistic solution, because it changes the effective density of the air, regardless of air pressure. Water vapour molecules are actually lighter and less dense than air molecules, so high RH decreases the air density. The effect of RH on air density is minimal, though, compared to pressure and temperature.

The way DA simplifies things, is that there are devices that use sensors to take the measurements and spit out a DA number for you to enter into your ballistic app. That way you don't have to manually take 4 measurements and enter each in separately. If your ballistic app is equipped with on-board sensors to take all necessary measurements, then it doesn't matter which air density calculation standard you use, except that you need to remember that the fewer measurements you can take, the better, as each measurement introduces error into the calculation. So measuring absolute/station pressure directly is better than taking a barometric pressure measurement and then calculating the station pressure using a temperature and altitude measurement.

Right, I agree that RH affects air density. That is why I am not confident that station pressure fails to account for it, but again I’d have to go to some references. This is not a thing I’ve had occasion to calculate, at least not for a long while. Talking about the calcs was my attempt to make sure we don’t assume either too much or too little about one another’s thinking.

My point is that the maximum number of measurements one needs to make and possibly enter is two: station pressure and perhaps RH. If the ballistic solver is forcing entry of temp and alt on top of station pressure, then it’s programmers may be ignorant of what is needed to properly compute the solution(?).

DA _may_ simplify that by one item. However, it looks very much like trying to work around an elaborate set of work-around a that we’re already used to using, that most don’t understand we don’t need to bother with. Just use station pressure and _maybe_ RH and be done. No more equipment to buy, no more elaborate gobbledygook that wows is with technical nonsense that, in the end, just makes a ton of calculations in one direction merely so that the same calcs can be run the other way before spitting out an answer. To me, entering 1 or 2 parameters and dropping the pretense is much simpler and easier than entering for sure only 1, but requiring yet more equipment or calculations and reference tables.

Perhaps we all have our own notions of what constitutes simplicity and ease.

So we can input 3 variables- absolute pressure, RH, and temp, we can enter 4 variables- baro pressure, altitude, RH, and temp, or 2 variables- DA and temp.

I agree. It doesn't matter which method you use. It just saves time and complication in the field if you're required to enter fewer inputs. I'm not saying one way is better than the other as long as the process and inputs are simplified and minimized. I've always used abs. pressure, temp, and RH method up until now, because my Kestrel doesn't measure DA and my phone has an integrated pressure sensor, but now that I have that DA app, I may start using that. We'll see. Really, I'm either entering DA and temp, or abs. pressure and temp. I leave RH set at 50% unless I'm shooting beyond 1000, given how little impact it has on the shot solution.

Actually if you use DA, you shouldn't need to enter temp, because it's already part of the DA calculation.

Ballistic AE does still ask for temp, but it's only for converting velocity to a mach number, I think for estimating the transonic region. Changing the temp value with a consistent DA input shouldn't have any effect on the drop values, if I understand what Ballistic AE is doing.

Hey fred, "formillous" posted this thread because a few people asked him to. Not everyone was born with a mil taped to their forehead.

Actually if you use DA, you shouldn't need to enter temp, because it's already part of the DA calculation.

Smoke everyone here could learn a bunch from formillous just fun that it’s needed to explain the most simple aspects of reticle use. It was in no way a shot at him but the guys that requested crack me up.

So, Yondering, do you know: Since RH impacts air density, doesn't station (absolute) pressure account for it, and thus the only thing the ballistic solver needs is station pressure?

Are you guys still thinking in terms of inches of correction to make?

Like clockwork.

This is generally what happens within a day or two when die hard MOA users learn to use both MOA and mils correctly-


"Wow both are just numbers that I spin to and they both work the same"

and then

"Wow, you know mils is easier to see and count on the reticle"

and then

"Wow, the drop corrections are easier to remember in mils"

and then

"Wow, wind brackets are easier with mils"


And then....



"I'm selling all my MOA scopes".





Seen't it. DOZENS of times.