A facile location of goniometer tilt-axis position with respect to a single-crystal electron-diffraction pattern orientation

For single-crystal electron-diffraction studies requiring definition of the location of the microscope goniometer tilt axis with respect to the diffraction pattern orientation, a quick calibration can be made taking advantage of the methylene O⊥ (001) subcell diffraction pattern obtained from any of a certain series of isostructural long-chain compounds when they are tilted 30° about the monoclinic b* axis. Those crystals giving a symmetric O⊥ (001) diffraction pattern when the stage is tilted 30° have their b* axes parallel to the tilt axis.