As described above, the Representative Frequency is used in variouscalculations within the OT e.g. to plot the field of views of theindividual telescope pointings in the Visual Spatial Editor. Regardingthe Control and Parameters section of the OT, its most importanteffect is on the estimated time. This is because this frequencydetermines the atmospheric opacity that will be used in thesensitivity calculation. If you are observing in a part of thespectrum that has very uneven opacity, it is possible that the OT'schoice for this parameter will not be optimal as no single value canapply to all the spectral windows.
If Up to 4 spectral windows has been selected in the SpectralSetup form, the OT currently sets the Representative Frequency to thefrequency of the first spectral window in the table. Therefore, youshould always try and enter your main line of interest first and addadditional lines after this i.e. further down the table. If Single Continuum has been requested, it simply sets it to thatfrequency. We strongly recommend that you view your spectral setup inthe Visual Spectral Editor as this will illustrate very clearlywhether your spectral windows lie in a region of strong and unevenatmospheric absorption.