French gold pendant watch with experimental balance Circa 1840

Gold lady’s cylinder pendant watch by Breguet
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A fine and very rare French 18 Carat gold cylinder pendant watch with experimental balance, circa 1840. Petite simple plate concentrique nouveau calibre. Sold to Madame la Maréchale de Lauriston on 30 April 1840 for 1300 Francs.
Early brass bar calibre movement, six jewels, cylinder escapement, steel escape wheel, unusual three arm uncut superimposed bimetallic platinum and blued steel balance, blued steel balance spring, parachute shock protection on the top pivot. Matte silver dial engraved with a neo Gothic rosette in the centre, champlevé Roman numerals, outer minute dot divisions and original gold Breguet hands. Case by Leopold Secheret, engine turned back, winding and setting apertures, engine turned band with a provision for regulation at 10 o’clock, wound and set from the back with a male key.
Dial signed and numbered inside the back cover and stamped with casemaker’s mark and French 18 Carat gold mark.
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Diameter: 29.5 mm
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Signed: Breguet 
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This watch employs a very unusual, apparently experimental balance; the top part is made of steel and is fused to the platinum bottom.
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Leopold Secheret, the case maker, entered his mark in Paris in May 1834. He was the case maker Breguet Neveu most used.
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Madame la Maréchale de Lauriston was the wife of Jacques Law, Marquis de Lauriston (1768 – 1828), Aide de Camp to Napoleon Bonaparte in 1800 and 1805, and Ambassador to Russia in 1811. She nominated Maréchal de France by Louis XVIII. He participated in the 1823 Spanish expedition.