RSpec is the peak reflectance measured over a very narrow angular band in the specular direction (+/-) 0.0991º.
RSpec is very sensitive to any texture that is present on a surface. This texture or waviness acts as a concave or convex reflector that deflects light around the specular angle. When RSpec is equal to the gloss value the surface is smooth, as texture increases the RSpec value decreases.
The diagram above shows the same coating applied to two panels, the first has orange peel/waviness present due to the incorrect application setting on the spray gun.