~ is a dimensional constant, called Planck’s constant, the value of whichdepends on what units one uses for time and for energy. It has the dimensions[energy] · [time] and its experimental values are1.054571726(47) × 10−34Joule · seconds = 6.58211928(15) × 10−16eV · seconds(eV is the unit of “electron-Volt”, the energy acquired by an electron movingthrough a one-Volt electric potential). The most natural units to use for quan-tum mechanical problems would be energy and time units chosen so that ~ = 1.