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A new approach for the measurement of red blood cell velocity at the level of microcirculation has been developed and characterized. The new real-time and automated measurement system is based on the dual-slit methodology, and blood flow information is extracted from images and transduced into two analog photometric signals and then processed using a hybrid analog-digital system that performs the cross correlation of the signals in real time. The characterization of the system consists of a calibration with a known velocity target, yielding to the hyperbolic calibration curve velocity versus delay and the determination of the velocity detectable range from 0.3 to 120 mm/s. A theoretical study of the measurement uncertainty and parametric studies were carried out to test the system robustness to changes of parameters and to determine the optimal configuration that is applicable to various experimental conditions. The system was further tested in in vivo experiments in the rat cremaster preparation in different types of vessels and flow velocities to verify the consistency of the results, as compared with those from conventional measuring systems. In addition, the dynamic behavior of the system and its response to changes in the measured velocity were studied through a continuous velocity record that was obtained during an experimental procedure.