Optistruct 如何计算模型的质量？

今天做了一个例子是：OS-2020: Increasing Natural Frequencies of an Automotive Splash Shield with Ribs。结束时有这样一句话：We have seen that the frequency of the structure for the first mode has increased from 43.63 Hz to 84.88 Hz. How much mass has been added to the part (check the mass of your ribs in the mass calc panel in the Tool page)?
小弟不知道在哪里有这个mass calc，请问哪位大侠指导吗？QQ：657203487.多谢。