Mechanic
Defaults: IQ-5, Engineer (same)-4, or Machinist-5.
This is the ability to diagnose and fix ordinary mechanical problems. A successful skill roll will let you find or repair one problem.
You must pick a specialty from within one of these four categories:
Machine Type: Any one class of nonvehicular machine. Types include Micromachines (miniature machinery, invisible to the naked eye; TL9+), Nanomachines (molecular-scale machinery; TL10+), and Robotics (robots and automated factories; TL7+).
Motive System Type: Any one type of propulsion system, regardless of vehicle type. Types include Legged, Tracked, Wheeled, Rockets, and Reactionless Thrusters.
Power Plant Type: Any one type of power plant, no matter what it powers. Types include Clockwork, Steam Engine, Gasoline Engine, Diesel Engine, Gas Turbine, Fuel Cell, Fission Reactor, Fusion Reactor, and Antimatter Reactor.
Vehicle Type: The controls, hull, motive system, power plant, transmission, and even the paint job of one specific type of vehicle listed under a vehicle-operation skill such as Driving, Piloting, or Submarine.
Mechanic specialties default to one another at -4, although the GM may modify this for particularly close or distant specialties. The systems covered by each specialty vary by TL. For instance, Mechanic (Light Airplane) covers single-engine biplanes at early TL6, small private jets at TL7, and so forth.
Familiarity is very important here. For instance, Mechanic/TL7 (Light Airplane) covers both propeller-powered seaplanes and small private jets, but going from one to the other gives you -2 for an unfamiliar item (propelled-powered plane to jet) and -2 for an unfamiliar implementation (seaplane to regular plane), for a net -4 to skill until you familiarize yourself with all the differences.
Modifiers: -2 for an unfamiliar item within your specialty (e.g., a barge when you're used to battleships), or for an unfamiliar implementation (e.g., a powerboat engine when you're used to automobile engines); equipment modifiers.