A ship may also have two to three slots for rigs, which are modules that require no power grid or CPU, but instead require a ship resource called "calibration". Installing a rig is a semi-permanent action, as a rig cannot be removed from the ship without being destroyed. Rigs come in four sizes, small, medium, large, and capital, which roughly correspond to the size of the ship, and are used to affect other aspects of the ship such as maximum speed or cargo capacity, or to augment the capabilities of other modules installed in the ship. Most rigs also incur a penalty to a certain aspect of the ship; for example, armor rigs reduce the maximum velocity of the ship.