Zbrush | What is max angle in Group by normals under Polygroups?

Oh! and one more thing I forgot to fix. I need to delete the top surface of the skirt. After completing this video, I realised that I have not deleted the top surface of the skirt. So this is an additional video on how you can do it easily with Polygroups > Groups by normals.

Under Groups by normals there are a few options for us to adjust. This is the slider that sets the maximum range of angle, within which the polygon faces should be considered as one polygroup. So the threshold is 45 degrees. Below that angle one polygroup and above above that angle another polygroup. I have here only two surfaces. The first is the top of the cylinder and the second the sides. These two surfaces definitely exceeds 45 degrees and each shall have its own color.