Paths involving the ETC. ETC will probably be used in two main "modes" Explore mode. This is when the observer is in the initial stages of developing a proposal and wants to see if the observations in mind are feasible. The observer will start in the ETC and enter the necessary target and exposure information. Target: typically really only require a brightness (e.g., magnitude or flux). target name and RA,Dec could also be entered at this stage. the target name would identify the calculation on the plots and tabular output. the RA,Dec is useful if the observer is concerned about the effects of zodiacal light on the sky background. Exposure: This is the bulk of the required information, instrument, aperture, spectral element, exposure time and any other optional parameters which are relevant. The main output is the S/N and a confirmation to the observer whether the observation is feasible. The target and exposure information entered by the observer in the ETC could be used to partially fill target and exposure templates assuming the observer is satisfied with the S/N. tweak and check mode: In this mode, the observer is well on the way to developing a phase II proposal and makes small changes and wants to confirm that the change has not caused the S/N to fall below a scientifically useful threshold. The target and exposure information would already be filled in, in this case. Useful entry points to the ETC would be from the target editor, the exposure editor, and the orbit planner, since these are the places where the properties of a target or exposure would normally be edited. The information returned from the ETC would be the S/N of the modified exposure. (There are plots and tables produced in the ETC, but these don't go anywhere in the proposal).