Urine specific gravity measurement is used to estimate the concentration function of the kidney, but the degree is poor and affected by many factors. The measured values are for reference only. When 1 gram of urine protein or glucose is contained per 100 ml of urine, the specific gravity of urine can be increased by 0.003 and 0.004, respectively, and attention should be paid to correction when measuring. In theory, the urine temperature compared to the temperature specified by the hydrometer (standard temperature 15 ° C) rises or falls to 3 ° C, then the specific gravity of urine should be increased or decreased by 0.001. The hydrometer must be corrected with distilled water before determining the specific gravity of urine.