A transport system for an automatic sample testing machine comprising, in combination: (a) a carrier having a plurality of holding features (202, 206), the holding features (202, 206) being arranged for holding a plurality of test sample devices and associated test tubes for containing a fluid sample; and (b) a drive subsystem for moving said carrier through said automatic sample testing machine, said drive subsystem comprising a reciprocating motor-driven block for engaging said carrier and moving said carrier back and forth in a predetermined longitudinal path, said path having a first end and a second end, said path arranged to extend along a longitudinal axis from an entrance station to a plurality of processing stations (400, 500) in said automatic sample testing machine, wherein said plurality of processing stations (400, 500) are arranged to be accessed as said carrier is moved along said path; characterized in that: the carrier further has a plurality of optical position tracking features formed in said carrier, each of the optical position tracking features being formed in alignment with one of the holding features (202, 206) for holding a test sample device and an associated test tube; and the transport system further comprises a plurality of carrier position tracking sensors (1050A-C) placed along said path for optically detecting the optical position tracking features on said carrier as said carrier is moved along said path, wherein each of said sensors (1050A-C) is arranged to be positioned at a predetermined location relative to an associated processing station (400, 500), and wherein the sensors (1050A-C) are arranged for (i) continuously monitoring the position of the carrier and (ii) detecting the location of the corresponding holding features (202, 206). (a) a carrier having a plurality of holding features (202, 206), the holding features (202, 206) being arranged for holding a plurality of test sample devices and associated test tubes for containing a fluid sample; and (b) a drive subsystem for moving said carrier through said automatic sample testing machine, said drive subsystem comprising a reciprocating motor-driven block for engaging said carrier and moving said carrier back and forth in a predetermined longitudinal path, said path having a first end and a second end, said path arranged to extend along a longitudinal axis from an entrance station to a plurality of processing stations (400, 500) in said automatic sample testing machine, wherein said plurality of processing stations (400, 500) are arranged to be accessed as said carrier is moved along said path; the carrier further has a plurality of optical position tracking features formed in said carrier, each of the optical position tracking features being formed in alignment with one of the holding features (202, 206) for holding a test sample device and an associated test tube; and the transport system further comprises a plurality of carrier position tracking sensors (1050A-C) placed along said path for optically detecting the optical position tracking features on said carrier as said carrier is moved along said path, wherein each of said sensors (1050A-C) is arranged to be positioned at a predetermined location relative to an associated processing station (400, 500), and wherein the sensors (1050A-C) are arranged for (i) continuously monitoring the position of the carrier and (ii) detecting the location of the corresponding holding features (202, 206).