The cRb-Clock is the world’s first commercially available portable cold Rubidium microwave atomic clock. The clock is designed for high frequency stability in the short term of 7×10-13/√τ and excellent long term frequency stability of 2.9×10-15 at one day and typically 2 x 10-15 at 10 days. With this level of performance the cRb-Clock can be used as a substitute for Hydrogen masers. The cRb-Clock, does not require calibration since there is no long term frequency drift and has an accuracy of a few parts in 10-15.