  We present a new scheme to detect and visualize oscillations of a single
quantum system in real time. The scheme is based upon a sequence of very weak
generalized measurements, distinguished by their low disturbance and low
information gain. Accumulating the information from the single measurements by
means of an appropriate Bayesian Estimator, the actual oscillations can be
monitored nevertheless with high accuracy and low disturbance. For this purpose
only the minimum and the maximum expected oscillation frequency need to be
known. The accumulation of information is based on a general derivation of the
optimal estimator of the expectation value of a hermitian observable for a
sequence of measurements. At any time it takes into account all the preceding
measurement results.
