The fitting skills are a group of skills that improve a capsuleer's ability to fit modules to ships, either by increasing the ship's CPU and Power Grid or by decreasing the CPU and Power Grid use of modules. While they do not directly improve a ship's performance, they allow fits that vastly outperform the options available to a capsuleer without them.
There are two skills that improve the CPU and Powergrid output of every ship. New capsuleers start with these skills at rank 3, and training them to rank 5 should be an early priority. A third skill, Jury Rigging, unlocks powerful options through the use of rigs.
CPU Management increases a ship's CPU output by 5% per level.
Power Grid Management
Power Grid Management increases a ship's Power Grid output by 5% per level.
Jury Rigging helps with fitting in several ways. First, it allows the use of rig slots, which are important to getting the most out of a ship. Second, it unlocks rigs that improve Power Grid (Ancillary Current Routers) and CPU (Processor Overclocking Units). These rigs are usually preferred to the equivalent lowslot modules when a fit needs a bit more PG or CPU to function.
Other Fitting Skills
These skills are all useful in some way, but their usefulness depends more on what types of ships a capsuleer flies than the three skills above. A well-rounded pilot is likely to reach rank 5 in all of them, but a specialist may find that some are not applicable to their situation.
Advanced Weapon Upgrades
Advanced Weapon Upgrades decreases the PG use of weapons by 2% per rank. This is a high priority skill for PvP pilots, as many fits require several ranks in the skill to make their PG fit. This is particularly the case for ships that use medium and large guns, as the weapons are usually the primary PG users on those ships, and for fits that use tech 2 guns. Rank 5 is a prerequisite for Marauders.
Capacitor Management is an extremely useful skill, but it does not directly improve a ship's fitting space. It is included here because it unlocks Micro Auxiliary Power Cores, which provide a fixed bonus to a ship's PG. These modules are preferred for frigates and destroyers, where the percentage bonuses from rigs and other lowslot modules do not provide as much benefit to their inherently limited PG.
Electronics Upgrades unlocks three types of modules (Co-Processors, Signal Amplifiers, and Sensor Backup Arrays) and decreases their CPU use by 5% per level. Co-Processors use a single unit of PG and increase a ship's CPU output. Signal Amplifiers increase a ship's locking range and scan resolution, allowing targets to be locked faster and at greater distances. Sensor Backup Arrays increase a ship's sensor strength, protecting against ECM. None of these modules are common, however, and the two that use any CPU at all are not major drains on a ship's fitting space, making this skill a lower priority for most new capsuleers than other fitting skills. In the long run, rank 5 unlocks the powerful Covert Ops and Recon ship skills, a strong incentive to eventually train the skill all the way.
Energy Grid Upgrades
Energy Grid Upgrades unlocks modules that effect a ship's Power Grid output and capacitor. It also reduces the CPU use of these modules by 5% per level. The capacitor modules are common on logistics ships, and some logistics fits require Energy Grid Upgrades 5 to fit everything. The PG modules are sometimes used to make an otherwise impossible fit work (although an Ancillary Current Router rig is usually the preferred option), and they can be a useful temporary solution for capsuleers who haven't yet trained the skills needed to make tight fits work. Energy Grid Upgrades 5 is a prerequisite for the Marauder and Heavy Assault Cruiser ship skills.
Shield Upgrades unlocks shield extenders, shield rechargers, and shield resistance amplifiers and reduces their PG use by 5% per level. Shield Extenders are found on most shield buffer tanks, and their PG use is quite high, particularly for smaller ships. Resistance amplifiers and shield rechargers are rarely used, and their PG use is minimal. Rank 4 is highly recommended for capsuleers who use shield buffer tanks, as it unlocks tech 2 extenders and drastically reduces their fitting requirements; rank 5 is needed for some fits.
Weapon Upgrades decreases the CPU use of weapons by 5% per level and unlocks damage upgrades for turrets and launchers. Rank 4 is a prerequisite for Advanced Weapon Upgrades (and the T2 variants of all damage-boosting low slot modules), making the skill a high priority. Rank 5 is a prerequisite for Heavy Assault Cruisers; most capsuleers will need Advanced Weapon Upgrades before HACs are a realistic option.