  In their activity, the traders approximate the rate of return by integer
multiples of a minimal one. Therefore, it can be regarded as a quantized
variable. On the other hand, there is the impossibility of observing the rate
of return and its instantaneous forward time derivative, even if we consider it
as a continuous variable. We present a quantum model for the rate of return
based on the mathematical formalism used in the case of quantum systems with
finite-dimensional Hilbert space. The rate of return is described by a discrete
wave function and its time evolution by a Schodinger type equation.
