A divergence-based procedure for diagnosing development, based on a two-layer model of the atmosphere, is discussed. It is pointed out that thinking in terms of vorticity advection and thermal advection is directly equivalent to considering divergence due to advective and isallobaric components of the ageostrophic wind. It is shown that such an approach is similar in basis to the quasi-geostrophic omega equation, but it is argued that it is more suitable for subjective application. However, simply estimating vertical velocity or instantaneous pressure tendency from synoptic charts is of questionable accuracy and little operational use, especially since such diagnostics are much more reliably obtained from NWP models. It is necessary to think in terms of the development and movement of features in the flow of the upper as well as the lower troposphere, and their vertical interactions.