  2D and 4D transverse phase-space of a low-energy ion-beam is measured with
two of the most common emittance scanners. The article covers the description
of the installation, the setup, the settings, the experiment and the benchmark
of the two emittance meters. We compare the results from three series of
measurements and present the advantages and drawbacks of the two systems.
Coupling between phase-space planes, correlations and mitigation of deleterious
effects are discussed. The influence of background noise and aberrations of
trace-space figures on emittance measurements and RMS calculations is
highlighted, especially for low density beams and halos. A new data analysis
method using noise reduction, filtering, and reconstruction of the emittance
figure is described. Finally, some basic concepts of phase-space theory and
application to beam transport are recalled.
