The exact lower limit generally refers to the number itself minus 0.5. LZ pays attention to the calculation formula of that percentage, and Lb refers to the exact lower limit of the group where the percentage belongs, not the exact lower limit of the percentage. For the specific group where the percentage is located, it is to look at the percentage grade group whose cumulative times are greater than a certain percentage for the first time, and bring it into the formula for calculation with the precise lower limit of this group.