High signal to noise spectra are required in chromospheric modelling because chromospheric emission lines are formed in a boundary layer under conditions of NLTE and in non-hydrostatic equilibrium, as well as in multiple magnetically-controlled streams, with horizontal structure on several scales, and vertical velocity fields. To obtain useable estimates of energy dissipation with height the authors have obtained sequences of spectra from F8 to K5 and for stars of different activity levels. The authors outline the constraints such observations place on models and indicate theoretical and observational difficulties.