which is an eigenfunction of the momentum operator,
of: a one-dimensional quantum system consisting of a stream of particles represented by the spatial wavefunction which is an eigenfunction of the momentum operator,
given that: the average number of particles per unit length is the constant 
and their velocity is obtained from the momentum, 
is: the net number crossing a fixed plane per unit time, i.e. 
[P11.1]
has as its SI unit: 
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