 At facilities such as ISOLDE at CERN and TRIUMF in Vancouver, for instance, measurement techniques are now being extended to short-lived radionuclei that only occur naturally in the interior of exploding stars.Their short half-lives and very low production rates at even the most powerful facilities require the very highest in sensitivity of such measurements.Penning traps, the central element in modern high-accuracy high-sensitivity mass measurement installations, enable measurements of accuracies approaching 1 part in 10^11 on single ions.