In modern manufacturing, quality is the main concern for manufacturing organizations. Technology advancement in manufacturing enables to scale down the critical dimensions of parts with the increase of part geometric complexity. This situation poses new challenges in quality control of a product. A high-quality product guarantees part interchangeability among manufacturers. To guarantee the quality of a product, tolerance verification has to be carried out in accordance with the product’s design specifications to decide whether the product/part conforms to the specifications or not. The tolerance verification process for dimension and form should be carried out by means of coordinate metrology. In coordinate metrology, traceability is the main issue in order to obtain a reliable measurement result. In this book, aspects regarding the traceability of focus variation microscope (FVM) for form measurements will be addressed: 1. What is performance verification for FVM? 2. What are the error sources which influence measurement uncertainty of FVM measurements? 3. How is it possible to estimate "task-specific" uncertainty of FVM measurements?