A more precise value of this quantity, which may be found using a watt balance, would allow a better definition of the kilogram. In CGS units, the electron's charge squared, divided by the speed of light, divided by this quantity, equals the fine structure constant. The de Broglie wavelength of a particle can be found by dividing this quantity by the particle's momentum. When this constant, which is the quantum of action, is divided by twice pi, it is shown with a bar through it. For 10 points, 
A more precise value of this quantity, which may be found using a watt balance, would allow a better definition of the kilogram. In CGS units, the electron's charge squared, divided by the speed of light, divided by this quantity, equals the fine structure constant. The de Broglie wavelength of a particle can be found by dividing this quantity by the particle's momentum. When this constant, which is the quantum of action, is divided by twice pi, it is shown with a bar through it. For 10 points, name this physical constant, symbolized h and named for a German.
A more precise value of this quantity, which may be found using a watt balance, would allow a better definition of the kilogram.
Planck's constant [prompt on h]