This paper introduces the research results on the influence of the trial weight in single-plane rotor balancing, where only the results of measuring the vibration amplitude of the device are used. In other words, there is no need to determine the phase during the balancing process. In the first section, the theory of single-plane rotor balancing using amplitude only will be summarized. This method is also known as the four-test run method or the three-point method. In the next section, an experimental balancing device is used to evaluate the influence of the trial weight on the results during the balancing process using the above method. The results and discussions on the influence of the trial weight will be presented and then applied to balance industrial equipment. The research results show that a reasonable calculation and selection of the trial weight will bring efficiency and safety in the process of handling unbalanced equipment.