Mould level variations, which are a significant cause of slab downgrading and production troubles at the continuous casters, can result from bad performances and low reliability of control equipments. A revamping project was realized at Dunkirk, after studies and prototype trials which enabled us to select the different components: stopper mechanism and actuating cylinder, level sensor, control electronics. A specific start-up organization, allowing for daily analysis of signals and results and frequent contacts with the engineering team, has permitted to reach quickly the targeted performances.