I first noticed this issue in SolidWorks 2012, and reported it to my VAR. Today, I noticed that the issue still occurs in SolidWorks 2015.

I have created five spheres using three different methods. Revolve with a vertical axis, revolve with a horizontal axis, sweep with a horizontal path, sweep with a vertical path, and the creation of a cube which is then filleted to form a sphere. Lofting a sphere should be possible, but it seems even more obtuse than sweeping or starting with a cube.

After slicing off the top and bottom of the resulting spheres, I measure the surface area of the remaining curved face, and the answers start to vary at the fourth decimal point.

I have increased the document image quality, the system option for curvature generation, and the accuracy option for Units/Precision.

I do not often need to calculate the surface area of a partial sphere to a high level, but a project brought this issue up again.

Ignore the swept spheres and the filleted cube, and help me to understand why the area of the partial hemisphere would vary between the two revolved options where the only difference is the horizontal or vertical orientation of the axis of revolution.

I've attached a screenshot and model of the 2015 file, as well as an older model showing similar results from SW2013.