Possibly unique Swiss five minute quarter repeater Circa 1860

Watch with early keyless Audemars stem winding and hand setting system 
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A very fine, unusual and possibly unique Swiss 18 carat gold open faced five minute quarter repeating lever chronometer pocket watch with early keyless Audemars stem winding and hand setting system, circa 1860. Frosted gilt movement, 31 jewels, Audemars keyless winding, wolf’s tooth winding wheels, gold wheel train, counterpoised straight-line lever escapement, cut bimetallic compensation balance with gold meantime and temperature adjustment screws, blued steel Breguet balance spring with overcoil, index regulator, repeating on gongs activated by a slide on the band. Gold hinged cuvette. White enamel dial with narrow Roman numerals, outer minute track, subsidiary seconds and origial blued steel Breguet hands. Case engine turned to the back, bolt between 10 and 11 for engaging the hand setting. Movement and case numbered.
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Diameter: 49 mm
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Signed: No name
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This watch is of extremely high quality and is notable for the unusual winding and setting system. In particular, it has a very individual and perhaps unique form of repeating. The hours and quarters are struck in the usual way, single blows for the hours followed by a double blow for each elapsed quarter hour. However a further single blow is struck for five minutes past the quarter and then a double blow for 10 minutes past the quarter. In other words this watch is a more advanced form of half quarter repeater distinguishing between and identifying the actual five minute intervals. For example, the time 2:20pm would repeat as follows: two single blows for the hours, a double blow for the quarter and a single blow for the five minutes past the quarter. However, 2:25pm would repeat as follows: two single blows for the hours, a double blow for the quarter and a double blow for the ten minutes past the quarter. This sequence is followed through for each quarter hour.