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Environmental Modifiers
Each effect is modelled physically, converted to angular error, and expressed as an absolute Target Number on the 3d6-exploding engine.
Granularity. One modifier point is worth about 8 percentage points near the median, so every band is roughly that wide. Note this is a statement about the median: out in the tails a point is worth 2 points or less, so the engine can express fine effects there. The claim that it "cannot express a 5% effect" is true only near TN 11.
Crosswind
Drift follows Didion's lag-time rule — it depends on the gap between real and vacuum flight time, not on flight time itself.
Crucially, wind drift is a systematic bias, not random scatter. Shooters dope it and fire-control computers measure it, so only the uncompensated residual degrades the shot. Each weapon below therefore uses its own dispersion and its own compensation.
Rifle round (850 m/s), Infantry rifle, trained, braced
| Wind | Raw drift @500 m | Residual after doping | Target Number |
|---|---|---|---|
| Calm (0 m/s) | 0.00 m | 0.00 m | 14 |
| Light air (2 m/s) | 0.42 m | 0.21 m | 15 |
| Light breeze (5 m/s) | 1.04 m | 0.52 m | 16 |
| Moderate breeze (10 m/s) | 2.08 m | 1.04 m | 18 |
| Strong breeze (15 m/s) | 3.12 m | 1.56 m | 20 |
| Gale (22 m/s) | 4.57 m | 2.29 m | lock req'd |
| Storm (33 m/s) | 6.86 m | 3.43 m | lock req'd |
Autocannon (1100 m/s), Autocannon, stabilised
| Wind | Raw drift @500 m | Residual after doping | Target Number |
|---|---|---|---|
| Calm (0 m/s) | 0.00 m | 0.00 m | 11 |
| Light air (2 m/s) | 0.09 m | 0.02 m | 11 |
| Light breeze (5 m/s) | 0.23 m | 0.05 m | 11 |
| Moderate breeze (10 m/s) | 0.47 m | 0.09 m | 11 |
| Strong breeze (15 m/s) | 0.70 m | 0.14 m | 11 |
| Gale (22 m/s) | 1.03 m | 0.21 m | 12 |
| Storm (33 m/s) | 1.54 m | 0.31 m | 13 |
Tank sabot (1700 m/s), Tank main gun, modern FCS
| Wind | Raw drift @500 m | Residual after doping | Target Number |
|---|---|---|---|
| Calm (0 m/s) | 0.00 m | 0.00 m | 5 |
| Light air (2 m/s) | 0.02 m | 0.00 m | 5 |
| Light breeze (5 m/s) | 0.04 m | 0.00 m | 5 |
| Moderate breeze (10 m/s) | 0.09 m | 0.01 m | 5 |
| Strong breeze (15 m/s) | 0.13 m | 0.01 m | 5 |
| Gale (22 m/s) | 0.19 m | 0.02 m | 5 |
| Storm (33 m/s) | 0.29 m | 0.03 m | 5 |
Light-speed weapons take no wind penalty at all, a real tactical difference rather than a genre convention.
Target motion and evasion
Required lead is v * t, and the error is the part of it the shooter fails to predict. But that error is bounded by what the target can physically do: displacement from a predicted path cannot exceed 0.5 * a_lat * t^2.
An earlier version omitted that bound and implied ground vehicles pulling nearly 20 g. With the bound in place, lateral acceleration matters more than speed — which is why a fighter is genuinely evasive and a frigate never is.
Absolute Target Numbers at 500 m, stabilised autocannon.
| Target | Lateral g | Stationary | Predictable | Evading | Jinking |
|---|---|---|---|---|---|
| Light vehicle (20 m/s) | 0.8 | 4 | 6 | 10 | 10 |
| APC / tank (20 m/s) | 0.5 | 3 | 3 | 4 | 4 |
| Light mech (20 m/s) | 0.6 | 3 | 3 | 5 | 5 |
| Aerospace fighter (250 m/s) | 9 | 3 | 9 | 13 | 13 |
| Frigate (100 m/s) | 0.5 | 3 | 3 | 3 | 3 |
Speed alone is not protection — sustained lateral acceleration is. A frigate at 100 m/s is easier to hit than a fighter at 250 m/s, and the gap is not about velocity.
What guidance actually buys
Against a jinking aerospace fighter at 500 m:
| Weapon | Dispersion | Lead compensation | Target Number |
|---|---|---|---|
| Missile, terminal guidance | 0.02 mrad | 100% | 3 |
| Capital gun, full fire control | 0.05 mrad | 90% | 11 |
| Tank main gun, modern FCS | 0.2 mrad | 80% | 13 |
| Mech mount, gyro-stabilised | 0.3 mrad | 75% | 13 |
| Precision rifle, braced, optics | 0.4 mrad | 30% | 13 |
| Autocannon, stabilised | 0.6 mrad | 60% | 13 |
| Infantry rifle, trained, braced | 1 mrad | 20% | 13 |
| Infantry rifle, standing, stressed | 4 mrad | 10% | 16 |
| Sidearm, combat conditions | 12 mrad | 0% | 21 |
| Unaimed / suppressive | 30 mrad | 0% | lock req'd |
Guidance wins on two counts, not one: it tightens dispersion and it corrects during flight, which removes the lead-prediction error that dominates against a manoeuvring target. That is why point defence, ECM and decoys are the real battle — they attack guidance rather than accuracy.
Range estimation
Gravity drop is compensated by the sight; what remains is error from misjudging range. Removing it is most of what a laser rangefinder is for.
Standing human, braced rifle.
| Range | Eyeball (20%) | Optic (5%) | Laser rangefinder (1%) |
|---|---|---|---|
| 100 m | 5 | 5 | 5 |
| 300 m | 12 | 11 | 11 |
| 500 m | 19 | 15 | 14 |
| 800 m | lock req'd | lock req'd | 18 |
| 1200 m | lock req'd | lock req'd | lock req'd |
Visibility
Modelled as a reduction in resolvable outline. Empirical rather than derived, and flagged provisional.
| Condition | Effective size | Unaided | Thermal / active | Thermal recovers |
|---|---|---|---|---|
| Clear daylight | 100% | 14 | 14 | 75% |
| Overcast / dusk | 85% | 15 | 14 | 85% |
| Light rain / haze | 70% | 17 | 15 | 70% |
| Heavy rain | 55% | 19 | 16 | 50% |
| Fog | 35% | lock req'd | 21 | 15% |
| Legacy smoke screen | 5% | lock req'd | 15 | 90% |
| Multispectral smoke | 5% | lock req'd | lock req'd | 10% |
| Starlight, unaided | 25% | lock req'd | 14 | 95% |
| Total darkness, unaided | 5% | lock req'd | 14 | 95% |
Thermal does not see through fog. Mid-wave infrared in fog is barely better than the naked eye, because fog droplets are comparable to or larger than infrared wavelengths and scatter geometrically — roughly 100 dB/km against 3 dB/km for millimetre-wave radar. An earlier version of this table gave thermal a flat recovery in every condition, which was wrong. Darkness is the opposite case, and thermal recovers nearly all of it.
Note also that legacy smoke is transparent to thermal while blocking almost all visible light. Defeating thermal sights takes multispectral smoke, so an obscurant is at least two different materials with different tactical prices.
Exposure time gates everything
Nothing happens for the first 1.77 s of a target's exposure — the measured lag to notice, decide, acquire, settle and break the shot. Three independent derivations converge on 1.5-1.8 s. Aimed fire then runs about 3.5 s per round in field conditions.
| Target exposed for | Aimed rounds available |
|---|---|
| 1 s | 0 |
| 2 s | 0 |
| 3 s | 0 |
| 5 s | 0 |
| 8 s | 1 |
| 12 s | 2 |
| 20 s | 5 |
The first aimed round therefore lands at about 5.27 s. Instrumented trials measured mean time from target appearance to first round at ~5.4 s, which the model reproduces without being fitted to it — the two constants were taken from separate sources.
An exposure of five seconds or less yields no aimed shots at all. Popping up and dropping back is not a modifier, it is near-immunity — which is precisely why bounding movement works, why suppression that shortens exposure is worth more than accuracy, and why a system that lets anyone shoot anything on sight is modelling something that does not happen.
Suppression
Suppression does not require hits. It requires near misses, which is exactly the low-probability fire that a hit-only model throws away.
| Round passes within | Chance the target is suppressed |
|---|---|
| 0.5 m | 96.2% |
| 0.7 m | 89.9% |
| 1 m | 83.3% |
| 2 m | 70.5% |
| 4 m | 57.6% |
| 6 m | 50.1% |
| 10 m | 40.6% |
| 20 m | 27.8% |
At a realistic 2% hit chance per round, 114 rounds are needed for 90% confidence of a single hit — but a round landing within 6 m suppresses half the time. That gap is the whole argument for volume of fire, and it is why most rounds fired in real engagements are suppressive rather than aimed.