English silver pocket chronometer with power reserve Circa 1890

Interesting pocket chronometer with helical hairspring
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An interesting pocket chronometer with helical hairspring and power reserve indicator, made by the royal watchmaker James William Benson on 62 & 64 Ludgate Hill, London, England, circa 1890. The open faced case of this watch is crafted from silver and has a niëllo band, an exceptional crown which was especially made for the rare  movement. The white enamel dial has Roman hour numerals a subsidiary seconds dial at 6 o’clock, a power reserve indicator at 12 o’clock and blued steel hands. The numbered movement has a very rare chronometer escapement with a helical hairspring, a diamond end stone, a lever escapement and is inscribed: By special warrant to H.M. the Queen & H.R.H the Prince of Wales.
The dial and movement are signed.
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Diameter: 49 mm
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Weight: 108 g
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Signed: J.W. Benson, London 
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The movement was probably originally designed for a gold hunting case watch. The current silver case was made especially for this movement.