  We describe a method that uses Optical Transition Radiation (OTR) screens to
measure in a single shot the emittance of an electron beam with an energy
greater than 100 MeV. Our setup consists of 4 OTR screens located near a beam
waist. A fit of the 4 profiles allows the reconstruction of the Twiss
parameters and hence a calculation of the beam emittance. This layout has been
simulated using Mathematica to study its sensitivity to errors and using Geant4
to include effects due to the scattering of the electrons in the screens. Some
assumptions made in this document are conservative to allow for unexpected
experimental issues.
