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 …).