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The signature radius is, for all intents and purposes, how “big” a ship appears on sensors. While the signature radius does not describe how big the ship appears visually, most other aspects are governed by the signature size of the ship.
A ship's signature is generally related to its size (a frigate is smaller and has a smaller signature radius than a battleship), and while all ships of a certain size tend to have similar signature radii, there are three ship classes with notably smaller signature radii than their peers:
There are also two classes of ships with notably larger signature radii than similar ships:
As a rough guide:
Ship Class | Sig Radius |
---|---|
Capsule | 25m |
Shuttle | 25m |
Frigate | 35m |
Destroyer | 65m |
Cruiser | 125m |
Industrial | 185m |
Mining Barge | 210m |
Battlecruiser | 270m |
Battleship | 420m |
Jump Freighter | 2830m |
Carrier | 2950m |
Freighter | 3540m |
Dreadnought | 4150m |
Supercarrier | 11,900m |
Titan | 16,000m |
Signature radius is how EVE measures the 'size' of your ship. It determines three very important things:
The larger a ship's signature radius, the faster other ships can lock on. Locking speed also depends on the scan resolution of the targeting ship (the higher the scan resolution, the faster you can lock on). Generally speaking, small ships have small signature radii and high scan resolutions, whereas large ships have large signature radii and low scan resolutions.
This is EVE, so there will be maths. Mercifully this is some relatively simple maths (at least compared to things like the tracking formula).
Lock time = ( 10000 / scanRes ) / ( asinh ( sigRad ) )
scanRes is the scan resolution of your ship, sigRad is the signature radius of the enemy ship, asinh is a trig function, you don't really need to know the theory behind it. Beyond that it works on diminishing returns, as you add more and more the amount of change gets less and less.
As a quick example: A Megathron locking a Punisher
Lock time = (10000/95)/(asinh(38)) = 105.26 / 4.33 = 24.31
So that's approximately 24 second lock time.
A smaller signature radius can help to reduce incoming damage from turrets, missiles and bombs (the only weapon system that is not affected by signature radius is the smartbomb). You can find more information about this effect and the equations in the dedicated articles about Turret Damage, Missile Damage and Bombs.
There are no skills that alter the signature radius of your ship. However, there are several modules and combat boosters that will increase either your or your opponent's signature radius
Halo implants, Skirmish Warfare Link - Evasive Maneuvers, and X-Instinct Boosters can all reduce the signature radius of your ship.