Geodetic areas, as opposed to grid areas, account for the ellipsoid surface.
TPC uses the Double Meridian Distance method to compute geodetic areas, with each separate DMD computation being scaled by the mean course scale factor (accounting for both the elevation and the grid scale factor) for that computation. In this way, the same scale factor is used for both the distance of each course and the area of each course. Curve and spiral segment areas, where encountered, are scaled in a similar fashion.
This method yields acceptable areas for all grid, ground and geodetic distance types.