Example of the sphericity response matrix for a measured multiplicity of 25 charged particles at mid-rapidity. The events are generated using the PYTHIA6 tune ATLAS-CSC (pp collisions at$\sqrt{s}=7$ TeV) and then transported through the detector. Particles and tracks with $|\eta|\leq0.8$ and $p_{\rm T}\geq0.5$ GeV/$c$ are used.