Guides · Wind

Wind Angles and Clock Values: Where Half Value Goes Wrong

A 2 o'clock wind is 87% of full value, not half. We test the full, half and no value convention against the exact solution at 600 and 1,000 yards and show why direction errors hurt most in a near-headwind.

6 min readSolved with the Ballista engineUpdated October 2026

A 10 mph wind from 2 o’clock pushes a 6.5 Creedmoor 1.65 mil at 1,000 yards. A full-value 10 mph wind pushes it 1.90 mil. That’s 87% of full value. A common convention, half value for anything between the hours next to 3 and 9, holds 0.95 mil and misses by 0.70 mil, 25 inches. The wind speed was right. The arithmetic was wrong.

Clock values and what they stand for

Shooters describe wind direction on a clock face with the target at 12. Wind from 3 o’clock blows from right to left straight across the range, from 9 left to right, from 12 into your face and from 6 at your back. The “value” of a wind is the fraction of its speed that blows across the line of fire. That fraction is the sine of the angle between the wind and the line of fire:

full-value speed = wind speed × sin(angle from 12 o'clock)

Each hour on the clock is 30°. So 1 o’clock is sin 30° = 0.50, 2 o’clock is sin 60° = 0.87 and 3 o’clock is sin 90° = 1. The full solution agrees. Across both rifles, every range and every direction at least 15° off the nose or tail, the engine’s hold divided by the full-value hold stays within 0.7% of the sine.

The convention against the exact value

The common convention has three values: full at 3 and 9, half at 1, 2, 4, 5, 7, 8, 10 and 11, and none at 12 and 6. Here is what it does at 600 and 1,000 yd.

The convention is exact at 1 o’clock, because sin 30° really is one half. It is badly wrong at 2 o’clock. At 1,000 yd it under-holds the 6.5 by 0.70 mil and the .308 by 1.15 mil, about 42 in. That is enough to miss a 12-inch plate with a perfect speed call.

It also fails near the nose. A wind 15° off the nose has a value of 0.26. If you round it to “no value,” you leave 0.50 mil of hold out at 1,000 yd. Half-hour positions are where rounding hurts. At 1:30, sin 45° is 0.71, not one half; thinking of 45° as “halfway to full value” is the trap. At 2:30 the true value is 0.97, and calling it half is the worst row in the table: 0.89 mil short at 1,000 yd. The sine is not a straight line.

A better set of fractions to remember

You don’t need a calculator. Learn three numbers for the clock:

• 1, 5, 7 and 11 o’clock: half value (0.5).
• 2, 4, 8 and 10 o’clock: seven-eighths value (sin 60° is 0.866, and 7/8 is 0.875).
• 3 and 9 o’clock: full value.

For half-hour positions, 12:30 is a quarter (0.26), 1:30 is seven-tenths (0.71) and 2:30 is as good as full (0.97). With these, the largest error at any position in the table above drops to 0.06 mil at 1,000 yd.

Direction errors cost most near a headwind

Because the sine is steep near 0° and flat near 90°, a one-hour mistake in direction costs very different amounts depending on where the wind is. At 1,000 yd with the 6.5:

• Calling 3 o’clock when the wind is really from 2 costs 0.25 mil.
• Calling 12 o’clock when the wind is really from 1 costs 0.96 mil, 3.9 times as much.
• A wind that swings from 11 to 1 o’clock moves the impact 1.92 mil, as much as the whole 10 mph full-value hold.

So the wind that deserves the most attention is the one blowing nearly straight down the range. It looks harmless because most of its speed does nothing, but the part that matters flips sides with every small shift. A full-value wind is the easiest one to hold, because its direction barely matters.

Quartering winds

A quartering wind is both a crosswind and a head or tail wind. The head or tail part changes how long the bullet is in the air, and that changes drift slightly. In the engine, a front-quartering 1 o’clock wind gives the .308 50.4% of its full-value drift at 1,000 yd, and a rear-quartering 5 o’clock wind 49.6%. That difference is too small to dial.

The vertical is more interesting.

Two effects meet here. A headwind slows the bullet relative to the air, so it drops a little more; a tailwind does the opposite. A crosswind also lifts or drops the bullet slightly through aerodynamic jump: with right-hand twist, wind from the right moves the impact down and wind from the left moves it up. From the front right both effects push the impact low, so they add. From the rear right they work against each other. The details are in the headwind and aerodynamic jump article. Neither effect is large, but in a strong quartering wind at long range a click of elevation may be part of the answer.

The app’s clock

Ballista’s wind wheel sets the direction in whole hours and names the value under the wind label: “Full value” at 3 and 9, “Most value” at 2, 4, 8 and 10, “Half value” at 1, 5, 7 and 11, and “No value” at 12 and 6. The words are only a label. The solver uses the exact angle of the hour you set, so a 2 o’clock wind is solved at 87% of its speed, not half.

Routine for an angled wind

1. Decide where the wind is coming from on the clock, to the nearest hour or half hour.
2. Convert to a full-value speed: half at 1, seven-eighths at 2, full at 3. Use a quarter at 12:30, seven-tenths at 1:30 and full at 2:30.
3. Use your full-value hold for that speed, as covered in the wind drift article.
4. If the wind is near 12 or 6 o’clock, spend your time on direction, not speed. Watch for it crossing from one side to the other.
5. In a strong quartering wind past 800 yd, check whether elevation needs a click.