The source image data measured with the shot-to-shot sweep mode (upper-half) and the resultant kinetic energy spectra of Au 4f photoelectrons. The spectra were composed of 201 consecutive images. All of the source PE images were recorded as single-shot images (14 ms exposure time) while sweeping the kinetic energy from 705 eV to 725 eV with 0.1 eV step, and their X-projection summed up with adequate calibration. The red solid curve is the resultant Au 4f photoelectron spectrum with appropriate calibration. The blue solid curve, on the other hand, is a typical example of a resultant spectrum with inappropriate calibration.