Adding unnatural amounts of nucleons may create energy shells, stabilize heavy nuclei. Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an “island of stability” of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. A group of researchers now present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.