English chronometer with 30 hour power reserve indicator Circa 1874

Gold open faced lever chronometer 
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A very fine English 18 carat gold open faced keywind chronometer pocket watch with 30 hour power reserve indicator made by John McLennan in London, circa 1874. Polished and tiered case with an engraved monogram on the back, a gold cuvette and maker’s punch mark GAP for George Augustus Potter of Clerkenwell. Signed and numbered white enamel dial with radial Roman hours, an outer minute track, auxiliary seconds at 6 o’clock, 30 hour power reserve indicator at 12 and blued spade hands. Signed and numbered frosted gilt 2/3 plate movement with chain and fusee, engraved honour cyphers, screwed chatons, an English lever escapement, gold screw compensation balance, free sprung blued helical balance spring and chatoned diamond endstone on the balance.
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Diameter: 52 mm
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Weight:  130 g
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Signed: John McLennan London
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John McLennan, English watchmaker
John McLennan was born in 1814. He was a well known English watchmaker who also worked for Charles Frodsham and the McCabe family. His business was established at 6 Park Place, Highbury in London. McLennan won the award for ‘Great skill & General Mechanical Excellence in a pocket chronometer’ in 1862 for making the smallest pocket chronometer (∅ 26.4 mm) at the time, No. 2164, with an Up and Down display. This watch was sold for 265 Guineas to Mr Alexander Baird of Urie Castle. He died in 1886, at 72 years old.