Fast time variability is an important characteristic of black hole X-ray binaries (BHXBs) and a key ingredient in understanding the physical processes in these systems. BHXBs show a variety of X-ray spectral/variability states, representing different accretion regimes. It has been recently shown that the overall strength of the rapid variability is a good tracer of these states as well. Fast aperiodic variability is generally studied through the inspection of power density spectra. Most of the power spectral components are broad and can take the form of a wide power distribution over several decades of frequency or of a more localised peak (quasi-periodic oscillations, QPOs). QPOs have been detected in many BHXBs and are thought to originate in the innermost regions of the accretion flow around the black hole. Even though their origin and nature is still debated, the study of QPOs provides a way to explore the inner accretion flow around black holes and neutron stars. Few theoretical models have been proposed to explain the origin of QPOs, but only one has been proved to be promising so far, having shown good agreement with observations. I will present the results obtained testing the Relativistic Precession Model onto the black hole binary GRO J1655-40. We show that the predictions of the Relativistic precession model match to a remarkable accuracy the observed fast-time variability properties of the source and for the first time we could demonstrate that it is possible to measure with high precision the mass and the spin of black hole X- Ray binaries through the sole use of X-Ray timing.