2017 Honda Ridgeline. The Honda Ridgeline is a unique pickup that employs car-like unibody construction in place of the rugged but unrefined body-on-frame setup that underpins its competitors. As a result, the Ridgeline provides a more comfortable ride and better handling than most pickups while still offering decent towing and hauling capabilities.
The flatness tolerance references two parallel planes (parallel to the surface that it is called out on) that define a zone where the entire reference surface must lie. Flatness tolerance is always less than the dimensional tolerance associated with it. Tolerance Zone: Two Sets of Parallel Planes where the entire referenced surface must lie. Gauging / Measurement: Flatness is can be measured using a height gauge run across the surface of the part if only the reference feature is held parallel.
This separation is the amount of actual flatness error of measured surface-see Figure 3 in the attachment*. For your surface being in the same level both methods can be used, and-as you may expect-different results may happen depending on method chosen.