thd and TDD

Your meter can be configured to provide thd (total harmonic distortion using the total RMS value for the content rather than the fundamental content) and TDD (total demand distortion, the harmonic current distortion against the maximum demand of the electrical system).

thd = H_C / RMS *100%

TDD = H_C / Demand_Max *100%

For more information see Harmonics Measurement Module in ION Reference help.