Optical interferometry is being used more and more to solve metrology problems. It is important in giving an insight into the properties of the top surface whether it is a processed surface or a thin film coating This paper will discuss metrology issues and ways in which to solve them using autocorrelation. Autocorrelation now commonly used to extract spatial information from surface profiles. It is suitable for looking at processing issues and identifying any periodic errors. An example showing the use of autocorrelation to solve process issues in diamond turning is shown.