During commissioning of a high energy accelerator, global correction methods based on orbit measurements are commonly used to identify and correct magnetic errors. However,in recent years, methods that allow local determination of the magnetic errors are becoming more popular like the action and phase jump method. In this book, the fundamentals of the action and phase jump method are described, as well as experiments conducted to evaluate linear and nonlinear errors at RHIC interaction regions. Very precise measurement of skew quadrupole errors and gradient errors at RHIC interaction regions are shown and how these measurement were used to set the interaction regions skew quadrupole correctors. Finally, the nonlinear errors are also evaluated using the action and phase jump method showing very promising results specially with SPS orbit data. People working in accelerator physics, particularly in the optics commissioning of the accelerator will find the method presented in this book useful to localize, measure and correct magnetic errors, specially at the interaction regions.