Часовое дело. Часовые функциональные и нефункциональные камни
Название (англ.):
Horology; Functional and non-functional jewels
Описание (англ.):
Lays down the technical definition of 'functional' and 'non-functional' horological jewels. Natural and synthetic jewels are called functional jewels if they serve to stabilize friction and to reduce the wear-rate of containing surfaces of the components of a timekeeping instrument.