This standard replaced MIL-STD-10A and defines more than forty different parameters including RMS (root mean square), slope, skew, PSD (Power Spectral Density, which is the most comprehensive characteristic) and more. There is a significant improvement in this standard because it allows the characterization of machined surfaces, at different spatial frequencies, which is especially important in cases where the optics were produced using techniques that leave periodic marks, such as caused by diamond turning. For most uses it is sufficient to use RMS. In all cases, it is important to specify the range in which the calculation is performed because without defining the spatial frequency range in which the measurement is performed, this standard is meaningless.