13.1	Introduction

The information in this chapter will help you to select a detector, grating configuration, and observing aperture, and to develop your observing plan. For each grating, the following information is provided:

•	A brief description of the grating, with special considerations for its use.

•	Grating parameters, including the dispersion and plate scale.

•	Plots showing the available central-wavelength settings and the range of wavelengths covered by each setting and (for the FUV gratings) FP-POS position.

•	Plots and tables of sensitivities and effective areas as a function of wavelength.

•	Plots of signal-to-noise ratio as a function of STMAG, Fλ, and exposure time.

Note that the quoted sensitivities are estimates for mid-Cycle 21 (April 2014). The COS Exposure Time Calculator (ETC) will be updated as the instrument’s sensitivity continues to evolve. See the COS Web site for the latest information.