The arrangement can be used to monitor a space and if used with a second arrangement, whose directional mirrors are arranged to provide new sensing curtains adjacent the curtains of the first detector, the arrangement can determine the direction of movement of {HEAD ~ the object} passing through {TAIL ~ the space} 
passing through
The arrangement can be used to monitor a space and if used with a second arrangement , whose directional mirrors are arranged to provide new sensing curtains adjacent the curtains of the first detector , the arrangement can determine the direction of movement of { HEAD ~ the object } passing through { TAIL ~ the space }
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