How does PM5500 series meter calculates TDD (Total Demand Distortion)

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Is there a more detailed description of how the PM5000 series meter calculates TDD (Total Demand Distortion

Product Line
PM5500 series

Environment
Documentation

Resolution

Total demand distortion (TDD) is the per-phase harmonic current distortion against the full load demand of the electrical system
TDD indicates the impact of harmonic distortion in the system
For example, if your system is showing high THD values but a low demand, the impact of harmonic distortion on your system might be insignificant
However at full load, the THD value for the current harmonics is equal to TDD, so this could negatively impact your system
TDD (total demand distortion) evaluates the harmonic currents between an end user and a power source
The harmonic values are based on a point of common coupling (PCC), which is a common point where each user receives power from the power source
The meter uses the following equation to calculate TDD:

Where ILoad is equal to the maximum demand load on the power system and HC is Harmonics Count
Harmonic content (HC) is equal to the RMS value of all the non-fundamental harmonic components in one phase of the power system.
The meter uses the following equation to calculate HC: