How length of lower facets is measured in the Helium Polish?
There are several ways from different systems and tools to measure lower girdle facets.
Helium software supports measurement of the heights' ratio on projection to vertical plane - Depth girdle facets and measurement of the lengths' ratio on projection to horizontal plane - Length girdle facets. Detailed information you can read here
Values of parameters Depth girdle facets and Length girdle facets are present in a Full report for round brilliant on second page. Parameters Min, Max and Avg - among 16 values are on page 1.
To open report in the panel Scan polished diamond select from menu Report / Open report in MS Word / Full B&W report for round brilliant or Full color report for round brilliant.