Antique pillar dating
Technical sophistication on any level adds value to a clock.
These range from a simple calendar aperture or a strike/silent options (for an uninterrupted night's sleep) to rocking ship automatons and rolling lunar cycle (knowledge of the phase of the moon was of great importance when planning a journey during the hours of darkness) to annual calendar dials and the times of sunrise, high and low tides.
Typical 17th-19th century eight-day movements run on two weights suspended on a cable and pulley - one driving the hands and the other the striking mechanism - and require two keyholes for winding.
Thirty-hour clocks, generally less expensive when made (although in the 18th century still costing the equivalent of two years of a farm labourer's wages), were driven by a single weight.
Good clocks by eminent names such as Ahasuerus Fromanteel, Thomas Tompion, George Graham, the Knibb family, Joseph Windmills and John Ellicott will bring five- and six-figure sums on the occasions they come to the market.
But, across a typical year, only a small handful is likely to be available.
A connoisseur market also exists for those clocks designed for precision timekeeping.
These range from the simplest estate-made pine case and painted tin dial, to Boulle marquetry and silvered brass.
But both will typically reflect the fashions of the time and provide a clue to date. On a national scale this can be seen in the differences between circular dial clocks made in early 19th century Scotland, the potbellied Comtoise clocks from the Franche-Comté region of France and the white-painted Bornholm and Mora clocks from Scandinavia.
Most longcase clocks strike the time on each hour or fraction of an hour, but musical movements were a further sophistication and, by the Edwardian era, many longcase clocks, often with monumental revivalist case styles, housed triple weight-driven movements capable of quarter-striking with the Westminster, Whittington or St Michaels's chimes.
These high quality clocks, capable of high four- and sometimes five-figure sums a decade ago, are sometimes hampered by size but remain popular with the export market.