A system for measuring a signal emitted by the contents of each of a plurality of reaction receptacles (162 ') comprising: a carousel mounted so as to be rotatable about an axis of rotation, said carousel including a plurality of reaction receptacle stations positioned around the periphery of said carousel, each of said reaction receptacle stations being adapted for use with two or more reaction receptacles aligned in a radial orientation with respect to the axis of rotation of said carousel; a signal measuring device constructed and arranged to measure the amount of a signal emitted by the contents of a reaction receptacle (162 ') placed in operative proximity to said signal measuring device, characterized in that said signal measuring device is positioned with respect to said carousel such that said reaction receptacle stations are successively moved into a signal measuring position as said carousel is rotated about the axis of rotation of said carousel, said system further comprising a signal measuring device transport mechanism constructed and arranged to move said signal measuring device with respect to said carousel, said signal measuring device transport mechanism being constructed and arranged to move said signal measuring device in a generally radial direction with respect to said carousel to successively place said signal measuring device into operative proximity to each of the radially aligned reaction receptacles carried in said reaction receptacle station moved into the signal measuring position, wherein said carousel is controlled so as to successively present each said reaction receptacle station in a signal measuring position in which one of the radially aligned reaction receptacles carried in said reaction receptacle station is in operative proximity to said signal measuring device and said signal measuring device transport mechanism is controlled so as to move said signal measuring device with respect to said carousel to successively place said signal measuring device in operative proximity to each of the radially aligned reaction receptacles (162 ') carried in said reaction receptacle station moved into the signal measuring position. a carousel mounted so as to be rotatable about an axis of rotation, said carousel including a plurality of reaction receptacle stations positioned around the periphery of said carousel, each of said reaction receptacle stations being adapted for use with two or more reaction receptacles aligned in a radial orientation with respect to the axis of rotation of said carousel; a signal measuring device constructed and arranged to measure the amount of a signal emitted by the contents of a reaction receptacle (162 ') placed in operative proximity to said signal measuring device, characterized in that said signal measuring device is positioned with respect to said carousel such that said reaction receptacle stations are successively moved into a signal measuring position as said carousel is rotated about the axis of rotation of said carousel, said system further comprising a signal measuring device transport mechanism constructed and arranged to move said signal measuring device with respect to said carousel, said signal measuring device transport mechanism being constructed and arranged to move said signal measuring device in a generally radial direction with respect to said carousel to successively place said signal measuring device into operative proximity to each of the radially aligned reaction receptacles carried in said reaction receptacle station moved into the signal measuring position, wherein said carousel is controlled so as to successively present each said reaction receptacle station in a signal measuring position in which one of the radially aligned reaction receptacles carried in said reaction receptacle station is in operative proximity to said signal measuring device and said signal measuring device transport mechanism is controlled so as to move said signal measuring device with respect to said carousel to successively place said signal measuring device in operative proximity to each of the radially aligned reaction receptacles (162 ') carried in said reaction receptacle station moved into the signal measuring position.