Get the calibration of the transducer.
The transducer's calibration, i.e. 'US-600-3600' or 'SI-10-100', or "" if no calibration was loaded using the function LoadCalibrationFile. The first section is "US" or "SI", indicating whether this calibration uses metric (SI) or imperial (US) units. The first number is the force rating for this calibration, which is in Newtons if this is a metric calibration, or pounds if this is an imperial calibration. The second number is the torque rating for this calibration, which is in Newton-meters if this is a metric calibration, or Pound-feet if this is an imperial calibration.