Single generator x-ray machines, which are more commonly used than multi-generator machines outside of major airports due to lower costs, still provide an effective means of screening bags and packages but have some limitations. While these machines can automatically detect explosives by placing a red box around suspicious areas, the detection is not perfect and explosives may be missed if they are obscured by clutter or placed farther away from the generator. Proper training is needed to understand these systems' capabilities and limitations so that operators can effectively detect threats.