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An optical frequency standard is operated at PTB where the frequency of a laser is stabilized to the inter- combination transition (λ≈ 657 nm) in laser cooled Ca atoms. Previously the uncertainty resulting from the residual velocity of the cold atoms at 3 mK limited the fractional uncertainty to 2 × 10-14. We now apply a novel method for producing ultra-cold atoms (T ≈ 10 μK). The frequency of the intercombination line has been measured with respect to the Cs hyperfine transition over eight years and a first frequency measurement with ultracold atoms has now been performed where the contributions from the residual velocity become insignificant at that level of uncertainty. A fractional uncertainty below 10-15 is expected for the near future.