Degradation cause by ageing is one of the major problems in the power system equipment such as transformer and machine. A continuous assessment method is the new method on assessing the condition of equipment that had gained an interest lately compared to the traditional time-based maintenance. One of these methods is known as condition-based monitoring. This predictive maintenance with the aid of online monitoring provides an indication of the equipment's condition. The development of measurement technologies and data analysis techniques using computational methods have an advantage of saving time and improve safety. This paper will review computation methods using in the time domain monitoring to determine the condition of the equipment in detail. The computational method will be based on the user-friendly software as well as the response time taking in assessing the condition. In addition, DAQ performance also takes into consideration while using computational method. The study will conclude the best computational application for time domain monitoring.