The difference in rotation you see printed on the screen comes from the internal conversion of FQuat to FRotator. The conversion most likely doesn’t happen when you set the rotation of your meshes and even if it did a 0.000015 wouldn’t make any difference, the engine will only consider rotations in the first decimal places because anything else is imperceptible even on very high resolution monitors. I don’t know where your problem comes from (probably a lighting issue) but I am sure it doesn’t come from the rotation of your mesh.