The system composes of two kind of laser curtain to obtain the time interval of passed bullet.

整个装置由两套相同的激光光幕构成，用以获取弹丸通过两个光幕的时间间隔。

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Next door to the museum, visitors pass through a curtain of bullet shells to enter a guerrilla camp, re-constructed to provide a taste of daily life during the conflict.

BBC: A glimpse of El Salvador's guerrilla past