Historic British timepiece maker Thomas Mercer has created its first eight-day calibre, the TM0801.
The TM0801 has been put to work within one of the company’s chronometers.
The calibre has been created using a chain-fusée combination and has a Spring Detente escapement balance with helical spring that delivers excellent isochronism – when the time taken for a single swing is constant regardless of the angle of vibration.
Another first for Thomas Mercer is the Ovalising Balance used within the eight-day calibre. This solution features an invar bar that does not expand or contract with changes in temperature and which forces the balance into an oval shape; this, coupled with an uncut rim which reduces centrifugal errors, leads to a great reduction in residual middle temperature errors.
Thomas Mercer was founded in Clerkenwell, London, in 1858 but the company moved out to St Albans in 1874. This year