Precision-guied munitions (PGMs, smart munitions, smart bombs, guided bomb units or GBUs) are guided weapons intended to maximize damage to the target while minimizing civilian damage. Because the damage effects of an explosive weapon 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. Thus, even if some bombs miss, fewer air crews are put at risk and the harm to civilians is somewhat reduced. The creation of precision-guided munitions resulted in the renaming of older bombs as "gravity bombs", "dumb bombs" or "iron bombs".