A guided bomb (also known as a smart bomb, guided bomb unit, or GBU) is a precision-guided munition designed to achieve a smaller Circular error probable. Because the damage effects of explosive weapons fall off with distance according to a power law, even modest improvements in accuracy (and hence reduction in miss distance) enable a target to be effectively attacked with fewer or smaller bombs. Therefore, with guided weapons, fewer air crews are put at risk, less ordnance spent, and collateral damage reduced.