Longines. A rare steel openface split second chronograph pocketwatch with constant force escapement

SIGNED LONGINES, NO. 6803 2 145, CALIBRE 262, 1960S

Details

Longines. A rare steel openface split second chronograph pocketwatch with constant force escapement
Signed Longines, no. 6803 2 145, Calibre 262, 1960s
The nickel plated three-quarter plate movement jewelled to the centre with fast oscillating nickel steel alloy balance, Nivarox anti-magnetic hairspring with inner and outer endcurves and constant force escapement numbered 10401990, the brushed silvered dial with Arabic numerals, outer tachymetric scale, subsidiary dials for running seconds and 15 minute counter indicating half minutes, blued steel hands, two sweep centre seconds hands rotating once in 30 seconds and indicating tenths of a second operated by depressing the lockable winder and a second button in the band, in circular case with hinged back and cuvette, case, dial and movement signed
66 mm. diam.

Lot Essay

The 'constant force' mechanism consists of a small spring mounted on the seconds wheel and wound by the main gear train. It is this secondary spring which is supplying power to the escape wheel. As it is kept in virtually constant tension by the frequent winding, the power delivers to the escape wheel and balance is thus much more 'constant' than the usual gear train system.

This lot is offered with a photocopy extract from Schriften der Frennden Alter Uhren, vol. XXXII, 1993, describing the mechanism.

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