  Optical lattice clocks are at the forefront of frequency metrology. Both the
instability and systematic uncertainty of these clocks have been reported to be
two orders of magnitude smaller than the best microwave clocks. For this
reason, a redefinition of the SI second based on optical clocks seems possible
in the near future. However, the operation of optical lattice clocks has not
yet reached the reliability that microwave clocks have achieved so far. In this
paper, we report on the operation of a strontium optical lattice clock that
spans several weeks, with more than 80% uptime. We make use of this long
integration time to demonstrate a reproducible measurement of frequency ratios
between the strontium clock transition and microwave Cs primary and Rb
secondary frequency standards.
