When we deal with rotating machinery, in order to monitor the characteristic and quality of the rotating parts, common method is to sample the accelerometer signals using discrete time axis with constant time interval. However, in most of the cases, rotational speed of the machine is nonstationary. Therefore, the characteristic frequencies of interest (speed of the shafts, gears and bearings) are not constant. So, signals sampled evenly in time cannot be used directly for condition monitoring. In order to deal with these problems we need algorithms that are robust to changes in rotational speed. In this regard, Order Tracking and Synchronous Average are well-established algorithms.