There are lots of basic explanations on the Internet of the two most famous uncertainty principles, that of momentum-position and Energy-time, but I do not find any basic explanation of the action-angle uncertainty principle. I do not even know what angle (or what operator) is being referred to here. Could someone give me an experiment which corresponds to this principle? (That is, preparing a large number of particles in identical quantum states, measure (um, calculate) the action of one half, measure the angle (?) of the other half, get the corresponding statistical distributions, and multiply the respective standard deviations.) Thanks.