Weapons spread determines the accuracy of a ranged weapon in degrees. Formulas here were taken from the GECK wiki.
The total spread is the largest of the aim spread value due to the character aiming and the weapon spread value due to the weapon itself. Therefore, no matter how skilled you are with the weapon or what perks you have, your weapon will always have a slight amount of spread. The exceptions being weapons with 0 spread.
State effects combine multiplicatively.
- Crouching reduces spread by 40%. (multiplier: 0.6)
- Using Aim down sights reduces spread by 65%. (multiplier: 0.35)
- Accordingly, doing both reduces spread by 79%. (multiplier: 0.21)
Mobility effects are additive, but under the game's default settings, they always sum to 1, and hence simplify out to being ignored; if the appropriate game settings are tweaked, they can be used to apply different penalties across walking, running and remaining still.
Skill/Weapon Condition Effects
These combine additively, but by default, Weapon Condition is always 0, so only the Skill Effect matters; if the appropriate game settings are tweaked, weapon condition (from 0 to 100%) times a constant will combine additively with skill.
Limb Condition Effect
Damage to limbs increases (pre-perk) spread.
- ArmPenalty is 0 with no crippled arms, 0.5 when the right arm is crippled with a one-handed weapon, 0.25 with one arm crippled with two-handed weapon, 0.5 when both arms are crippled with two-handed weapons.
Weapon spread is equal to the Min Spread stat of the weapon in degrees. The weapon condition has no effect on the weapon spread.