A diamond-set platinum and rock crystal pendant fob watch by Cartier

A diamond-set platinum and rock crystal pendant fob watch by Cartier, c.1915, the circular dial with guilloche decoration, black Roman numerals and signed Cartier Paris, within a border of rock crystal and suspending from a diamond-set bar brooch with pendant loop, the reverse centred with a foliate quatrefoil design millegrain-set with diamonds and centred with a larger diamond within a border of millegrain-set circular-cut diamonds, further border of larger circular-cut diamonds, the bezel with initials F.J. within lozenge, French control mark and numbered 9020 to back of case, unsigned keyless-wind movement with club-tooth lever escapement, reverse of dial not inspected, 4cm wide, fitted case by Cartier