The invention relates to a flow cell for an ultrasonic flow meter comprising two transducers of ultrasonic waves wherein the two transducers are reversibly detachable from the flow cell. A comparator selects one of the target module addresses a function of a base address for a circular buffer, a length of the circular buffer, an index address and a modifier value. A distal end of each panel that is continuous with the respective longitudinal side edge is folded underneath and affixed to the barrier later of the main body to form a looping member and a freely extending flap. The true parameters are entered into the system and when the tracker is located in the 3D environment, the device can then be located in the 3D environment with a high degree of precision using the true parameters. The memory stores instructions that may be executable by a processor.