There are two basic floor categories: random traffic and defined traffic. Currently, fewer than 1% of the floors constructed in the US are classified as defined traffic. In very-narrow-aisle warehouses, forklifts travel 6-foot wide aisles between storage racks with the aid of rack-mounted rails or a wire guidance system embedded in the floor. While moving down the aisles, these lift trucks can raise their forks to retrieve or place products at various levels. For these forklifts to perform as intended, defined-traffic floors must be extraordinarily flat and level, or superflat.

Since the lift truck travels the same route over and over, the smoothness of the wheel paths in superflat aisles becomes extremely important. Although superflat slabs are placed in long, narrow strips approximately 15 feet wide, tolerance only needs to be confirmed in the wheel tracks. Each of the traffic paths should be directly measured, using a continuous-recording floor profilometer configured to run exactly in the wheel tracks.

The Fmin is a direct measurement of the floor surface in the wheel paths of the vehicle for which the defined-traffic area was designed. An Fmin100 specification is a baseline number corresponding to a flatness tolerance of 1/8 inch in 10 feet. Lower defined-traffic area tolerances result in lower Fmin requirements (for example, an Fmin of 50 corresponds to 1/8 inch in 5 feet).