The Spectral Editor's graphical interface consists of two frequency axes, one above the other, with the space in between used to display various features of interest. The two axes themselves show the features in observed and rest frequencies, depending on the source velocity. The display can be zoomed using mouse clicks (left-click: zoom in, right-click: zoom out) or the scroll wheel, the zoom being centred at the location of the mouse pointer (magnifying glass symbol). Once the display has been zoomed, it can be panned by grabbing one of the horizontal green bars that appear whenever the mouse is somewhere within the graphical area. Additional zooming and panning controls are located below the graph, as well as a number of other controls.
Just below the observed frequency axis are hatched areas that show the available receiver bands. These are displayed in grey, apart from the currently-selected receiver band which is coloured blue (and doubly, compared to singly, hatched). The upper, wider part of the hatched area shows the full range of frequencies that can be observed using a band whilst a narrower rectangle below this shows the allowed range of the first local oscillator (LO1).
A prominent feature of the graphical interface is the transmission curve. This shows how much of the radiation from the source is actually received at the telescope and is calculated using the Atmospheric Transmission at Microwaves (ATM) code9.1 that is also used in the ALMA Sensitivity Calculator and for the OT time estimates. Years of monitoring have been used to determine the characteristic octiles of precipitable water vapour (PWV) at the ALMA site and the transmission curve corresponding to each can be selected manually, or the OT can automatically display the appropriate one. The latter is recommended as it is this value of PWV (or a very similar one) that will be used to trigger the observation of a project, based upon the spectral windows that have been defined in the Forms Editor, specifically by the Representative Frequency. Changing the displayed transmission curve is for experimentation only as it will not affect the conditions assumed for the observations and hence the OT's time estimates!
It is also possible to display spectral lines using the Spectral Line Selection Tool which is described in detail in Section 7.3.