How do I know if my floor is flat?

To find the clear floor using the F numbers, the elevation differences, d, between the ground points, a part of a straight line foot are measured. The differences, q, between all adjacent values are calculated. Therefore, use the standard mean and distance of the q values to determine the FF number.Using F-numbers, you can find the floor flatness by measuring the elevation differences between points on the floor. q is the difference between all of the d values. The FF number can be determined using the mean and standard deviation of the q values.