Helium help : Comprehensive list of report parameters
Culet

Applicable to any cuts

Culet diameters are measured in 360 directions with the step of 0.5 degrees (because opposite directions apply to the same diameter). The diameter of the culet in some given direction is measured as a distance between two parallel vertical planes placed perpendicularly to the given direction as close to each other as possible, so that all vertexes of the culet lay between these planes (similarly to usual diameter). The minimum, maximum and average culet diameters are calculated using this array of values.

DiamCalc Brilliant Cut Parameters