ATLAS is one of the largest and most complex science instruments ever built, designed to measure and identify particles coming from particle collisions. One of the most important measurements it makes is that of the energy of the particles. Stephen Goldfarb, ATLAS physicist (U of Michigan, USA) interviews ATLAS colleague Isabelle Wingerter-Seez, the Liquid Argon Calorimeter system project leader to find out how these measurements are made. The interview includes the following topics: the shape of the LAr calorimeter, what the LAr system is made of, construction and assembly of the LAr calorimeter, why the first collisions in the LHC were so exciting for scientists, what Wingerter-Seez hopes the LAr system will find. The video is concluded by Goldfarb giving a brief synopsis of the LAr system, its purpose and aims. Contains historical video clips showing when parts of the calorimeter were being delivered from abroad for assembly and installation at CERN. Produced by: ATLAS OUTREACH Director: Yves-Rene Kayonga Director: Claudia Marcelloni