The marine chronometer signed by John Lilley & son from 1929 has shown evidences of a failure of one of its major components. The helical hairspring which is co-regulating the frequency of the balance (factor determining the rate of the mechanism) was broken by fracture near its lower attachment point. The aim of the project was to provide a replacement spring for the chronometer which would possess the required mechanical properties (toughness, elasticity, shape, composition …).