  In preparation for the extraction of pseudoscalar meson photo-production
amplitudes from a new generation of complete experiments, we assemble the
relations between experimental observables and the Chew-Goldberger-Low-Nambu
amplitudes. We present expressions that allow the direct calculation of matrix
elements with arbitrary spin projections and uses these to clarify sign
differences that exist in the literature. Comparing to the MAID and SAID
analysis codes, we have found that the implied definitions of six
double-polarization observables are the negative of what has been used in
comparing to recent experimental data.
