Nerd stuff · Product physics
Do you need zero conditions in a ballistic calculator?
This is the feature we didn't build.
Quick answer
No, not for a rifle zeroed at 100 yards. The largest correction a zero-conditions form can produce anywhere on Earth is 0.07 MOA, a seventh of one scope click, which is why Wrist Dope doesn't ask for one. Zero-atmosphere inputs only start to matter for rifles zeroed at 300 yards and beyond.
Most ballistic apps ask for zero conditions: the temperature, pressure, and humidity on the day you zeroed. People ask us where that screen is in Wrist Dope. So we ran the question through our ballistics engine, and here is what that screen is actually worth.
0.01in
What summer-to-winter air does to a 100-yard zero at your home range.
0.07MOA
The most the zero-weather form can correct, between the two harshest shooting environments on Earth.
1/7click
That maximum, measured against one quarter-MOA click of your own turret.
The measurement
The signal is buried under your own noise
A zero is a measurement, and every measurement has a noise floor. We computed everything that nudges a 100-yard zero, from the atmosphere's contribution to the ordinary wobble of a range session, and put them on one scale. The two blue bars are the entire payload of a zero-conditions form. Look closely; they are easy to miss. That is the finding.
Things that move a 100-yard zero
Inches at 100 yards, .308 Win reference load. Blue is what a zero-weather form captures. Gray is noise every zero session already contains.
See the numbers
| Source | Shift at 100 yd (in) |
|---|---|
| Air: home range, summer → winter | 0.01 |
| Air: sea level → 10,000 ft desert | 0.04 |
| Group-center wobble, 1-inch rifle | 0.10 |
| A 3 mph breeze you didn't notice | 0.22 |
| Ammo cold-soaked to −40° | 0.24 |
| One click of your turret (1/4 MOA) | 0.26 |
| A 10 mph wind | 0.73 |
A 3 mph breeze you never noticed moves the bullet five times farther than the worst air swing the planet can produce. The statistical wobble of your own group center, on a rifle that shoots an honest inch, is about 0.10 in. The atmosphere's entry in your logbook drowns in both.
The form
Four fields, one seventh of a click
Zero atmosphere
Conditions when the rifle was zeroed
Temperature
Station pressure
Humidity
Altitude
Max effect: 0.07 MOA
anywhere on Earth, 100-yd zero
This screen, or one like it, ships in most serious ballistic apps. Fill in all four fields perfectly, from the best weather meter money can buy, and the largest correction they can ever produce for a 100-yard zero is 0.07 MOA. Your turret cannot dial it. Your rifle cannot group tightly enough to reveal it. No shot you will ever take can tell you whether it was applied.
Wrist Dope leaves the screen out on purpose. Fewer fields to fill wrong, nothing lost downrange.
The fair question
Then why does every other app ask?
Because the field is not useless in general. It is useless at a 100-yard zero. Zero-atmosphere inputs earn their keep in workflows where the zero itself is set far away, at 300, 400, or 500 yards, where the air has time to lean on the bullet before it ever reaches the target. There, the weather of zeroing day really does get soldered into your sights, and the form is how a solver un-solders it.
Conditions baked into your sights, by zero range
MOA of error carried between Earth's two extreme environments, split into the air's share and the ammo-temperature share. Hairline: one quarter-MOA click.
See the numbers
| Zero range | Air (MOA) | Ammo temp (MOA) | Total (MOA) | At 1,000 yd (in) |
|---|---|---|---|---|
| 100 yd | 0.07 | 0.26 | 0.33 | 3 |
| 200 yd | 0.30 | 0.57 | 0.87 | 9 |
| 300 yd | 0.73 | 0.92 | 1.65 | 17 |
| 400 yd | 1.42 | 1.32 | 2.74 | 29 |
| 500 yd | 2.45 | 1.78 | 4.23 | 44 |
At a 100-yard zero the whole stack sits at one click, and the air's slice is a rounding error. By a 500-yard zero the air alone is ten clicks, and now the form matters. So the choice is yours: zero far and do the bookkeeping, or zero at 100 and let the bookkeeping cease to exist. We designed for the second option, because it is also the more accurate one.
The part of the instinct that is right. The orange slices above are real, and they are the reason your buddy swears his zero "moves in winter." Cold powder leaves the muzzle slower, and unlike the air effect it keeps growing with distance: 9 inches at 600 yards for this load at −40°. But the fix is a chronograph session that measures your load's velocity against temperature once, not a weather diary at every zero check.
What we built instead
Weather belongs at the shot, not in an archive
The same atmosphere that moves your zero by hundredths of an inch moves a 1,000-yard impact by twenty feet between environments, and by feet across a normal season. That is where the environment deserves obsessive tracking: live, at the firing point, at the moment of the shot. So that is where Wrist Dope spends its effort, reading current conditions from your wrist and rebuilding your solution every time the air changes. One clean 100-yard zero from you, live atmosphere from us, and there is nothing left for a zero-weather form to do.
The only zero-day records that ever get used
- Zero range (make it 100 yards)
- Ammo and lot, with chronographed muzzle velocity
- Your load's velocity change per degree (one chronograph session, good for the life of the load)
- Date and round count (for wear and lot changes)
The takeaway
Zero conditions are noise. Shot conditions are feet.
Everything on this page points at one division of labor. The weather on the day you zeroed is worth hundredths of an inch, so nothing needs to remember it. The weather at the moment of the shot moves impacts by feet, so something has to measure it, where you stand, when you press the trigger. Guessing does not work: station pressure falls with every thousand feet you climb, the swing from a summer zeroing session to a cold late-season morning moves a 600-yard impact about the height of a deer's vital zone, and the weather app on your phone reports conditions from an airport, not your ridge.
That means some instrument at the firing point has to read the air: temperature, station pressure, and altitude, the three numbers that set the density your bullet actually flies through. A handheld weather meter does the job. A watch does it without being asked. Wrist Dope reads the barometer on your wrist for the true pressure where you stand, GPS for your altitude, and live local weather for temperature, then rebuilds your firing solution every time the air changes. Your clean 100-yard zero plus a sensor on your arm covers the atmosphere for you, with nothing to type and no card to reprint.
Common questions
- Do I need to enter zero conditions in a ballistic calculator?
- Not if you zeroed at 100 yards. The largest correction a zero-atmosphere form can produce anywhere on Earth at a 100-yard zero is 0.07 MOA, a seventh of one quarter-MOA click. Those inputs only earn their keep for rifles zeroed at 300 yards and beyond, where the air of zeroing day genuinely bakes into the sight setting.
- Should I write down the weather when I zero my rifle?
- At a 100-yard zero the atmospheric signal is 0.01 to 0.04 inches, far below the noise of your own groups, wind, and turret clicks. Record the useful facts instead: zero range, ammunition lot, chronographed muzzle velocity, and your load's velocity change per degree of temperature.
- Why does my rifle's zero seem to shift in winter?
- It's the ammunition, not the air. Powder burns slower when cold, so muzzle velocity drops; a temperature-sensitive load loses about 99 fps between a summer chronograph session and a −40° morning, which grows to 9 inches at 600 yards. One chronograph session across temperatures captures the number for good.
Want the full argument with the noise math and every table? Read the white paper: Should you record weather conditions when zeroing a rifle?