Nominal value scale and scale of the order of addition, subtraction can not be, but the value scale spacing can be addition and subtraction. However, since the origin is arbitrarily set, it can not perform multiplication and division. Such as a hydraulic motor, the difference between the hydraulic motor repair between 5 ℃ and 10 ℃, can be said between 15 ℃ and 20 ℃ difference is the same, are 5 ° C. But I can not say 20 ℃ is more than 5 ℃ 4 times higher temperatures. Meaning the ratio scale is absolute, meaning that it has a "no" amount of the origin 0. Length, weight and time are measured by the ratio of the scale range. The difference between the measured value and scale-ratio are comparable. For example: the difference and the difference between 10 minutes and 15 minutes of between 5 minutes and 10 minutes are 5 minutes, 10 minutes 5 times 2 minutes. The ratio of scale can be arithmetic operations. Hydraulic pump motor and the same point: 1) In principle, hydraulic motors and pumps are reversible, if drive motor, the output is hydraulic energy (pressure and flow) the hydraulic motor repair, which is a hydraulic pump; If the input pressure oil output is mechanical energy (torque and speed), it becomes a hydraulic motor. 2) From a structural point of view, the sale of the hydraulic motor, the two are similar. 3) From the working principle point of view, both of which are sealed work volume use changes were suction and discharge of oil. For the pump, the work volume increases suction, high pressure oil discharged work volume decreases. For hydraulic motor, work volume increases into the high pressure oil discharged low pressure oil work volume decreases. Different points of hydraulic motors and pumps: hydraulic motor maintenance, crystal creating a hydraulic quality assurance (certification), the hydraulic motor from Jinan Jing Chong Hydraulic Machinery Limited. Jinan Jing Chong Hydraulic Machinery Co., Ltd. (www.jnjcyy.com) (www.jnjcyy.com) Shandong Jinan, mining machinery leaders, over the years, the company is implementing the scientific management, innovation and development, the principle of honesty and trustworthiness, the maximum meet customer needs. In the crystal creating hydraulic leadership with the staff warmly welcome all inquiries negotiations to create the crystal creating hydraulic better future.