Test for finding the representative volume of interest (RVI-test), based on the Vv as the evaluation parameter and Conn.D as the control parameter for the air part. The optimal VOI size is found when the variation of the Vv and Conn.D are no longer affected by the varying size of the considered VOI. For the considered sample this occurred at 6 µm, at which length scale both the Vv and Conn.D have levelled out and reached a plateau, i.e. at the second plateau for the Conn.D. Note that no Conn.D values are provided for VOIs below 1.5 and 2.0 µm for VOI1 and VOI2, respectively, since the VOIs were too small for extracting an image skeleton, with nodes and branches.