The nuclide 187Re beta-decays to 187Os with a half-life of approximately 41.6 Gyr. The long half-life and simple relation between 187Re and 187Os makes the ratio a good candidate for a cosmic clock. In order to "use the clock" we must determine the production of 187Re and 187Os through chemical enrichment of the Galaxy. This is a complicated task with a large number of assumptions and simplifications involved. The uncertainties related to some of the uncertanties are investigated. A hydrodynamical simulation is approximated with a simple one-zone chemical evolution model. The physical parameters of the chemical evolution model is varied by generating random numbers with a gaussian distribution to emulate the uncertainty of parameters. I conclude that observational constraints on r-process nuclei does not affect the cosmochronology of the Re-Os system much. The Galactic history, like star formation and mass function over time, would have greater effect on the cosmochronology.