Beam energy measurement at a linear collider with an SLC style energy spectrometer

We discuss the energy measurement requirements for the physics program at a next generation linear collider. The SLC energy spectrometer and its performance are described. We conclude that there may be a use for a modification of this spectrometer in the extraction line, but that the primary energy measurement should be integrated into the accelerator. It will be difficult to achieve the accuracy desired for some of the physics objectives.