[en] Symmetry capsules or 'symcaps' are inertial-fusion capsules that resemble ignition capsules but lack cryogenic fuel. The shape of an imploded symcap, as revealed by images of its x-ray emission near stagnation, contains information about the degree of radiation drive asymmetry that drove its implosion. We have carried out many numerical studies of how symcaps perform, tested their response to variations in laser and target parameters, and conducted Omega experiments in 2007 to verify their operation in certain cases. Thus we are building confidence in the use of symcaps to achieve the critical goal of measuring and optimizing drive symmetry in NIF targets prior to the first ignition shots