Floor flatness -FF control the local bumpiness of the floor surface and is primarily affected by finishing operations after screeding, including restraightening and power floating. FF numbers evaluate the elevation differences along a test line at 1-foot intervals. F numbers start from zero to infinity so the higher the F number, the flatter the floor.
Floor levelness -FL control departure of floor surface from the specified slope or plane of the surface. FL numbers evaluate the elevation differences along a sample line at 10-foot intervals. The higher the FL number, the more level the floor.
FF-FL numbers are most difficult to achieve in hard to work areas such as around plumbing, narrow work areas and areas where equipment is hard to deploy.