Precision timing, measured with atomic clocks, is essential for global navigation satellite systems, telecommunications and other applications. The EU-funded CSOC project aims to develop the first chip-scale optical clock. The miniaturised optical clock will utilise the two-photon transition in the rubidium-85 isotope that vastly improves the signal compared to current atomic clocks relying on radiofrequency transitions. The project work will build on recent advances in Kerr soliton microcomb technology, picosecond mode-locked lasers and heterogeneously integrated on a chip as well as higher-efficiency chip frequency doublers achieved by the partners.