# Meaning of ECMWF model levels

I am trying to understand the actual meaning of the ECMWF L137 model levels. In the link I provided, both pressures (in hPa) and heights (in m) are given for every level. But which actually defines the model level, and which is merely included as an indicative value?

The vertical coordinate parameters define the edges of the atmospheric layers in terms of the surface pressure (in Pascals). The parameters can be considered as being true at the mid-point (in pressure) of a layer for each point. The formula to use to determine edges of the layers is $$P_{k+1/2} = A_{k+1/2} + B_{k+1/2}P_s$$, where $$P_s$$ is the surface pressure and $$A$$ and $$B$$ are defined in the table.