Swiss 18k gold repeater with split-seconds chronograph circa 1920

Gold open faced lever watch 
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A very fine and rare Swiss, 18K yellow gold, a keyless, minute repeating pocket watch with split-seconds chronograph and 30-minute register, circa 1920. A polished, hinged gold cuvette. White enamel dial, radial black Arabic numerals, outer minute track, outermost fifths of seconds divisions, red Arabic five minute/seconds numerals, subsidiary seconds at 6, 30-minute register at 12 o’clock. Blued steel Spade hands.
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A rhodium-plated movement, Geneva striping decoration, 29 jewels, counterpoised straight-line lever escapement, adjusted cut bimetallic compensation balance with gold and platinum screws, blued steel Breguet balance spring, swan-neck micrometre regulator, chronograph and split-seconds mechanisms set on the backplate, repeating on gongs activated by a slide on the band. Dial and case signed.
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Diameter: 48 mm
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Signed: Audemars Piguet  Swiss
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A similar watch is illustrated and described in Audemars Piguet, by Gisbert L. Brunner, Christian Pfeiffer-Belli and Martin K. Wehrli, 1993.