An apparatus for rapid thermal testing of samples consisting of a single sample chamber in which the samples are preferably arranged circularly around the opening through which a fluid of varying temperature, preferably air, is introduced to provide for rapid, uniform cooling and heating of the samples. The apparatus may include a statistics engine coupled to a memory. Anode side and cathode side current collector plates sandwich the stack of unit cells. The third guide member pivots between a third position in which a third contact surface thereof is in contact with the second contact surface of the second guide member in the first position, and a fourth position in which the third contact surface is separated from the second guide member. The system may also provide a method of flowmeter selection and billing.