THOMAS MERCER No. 24735: A two-day survey chronometer, dated 1963 with 24-hour dial and half-second make/break' electrical contacts, and 'start/stop' mechanism signed and numbered Thomas Mercer 24735, Arabic hour chapters, blued steel hands, subsidiary up-and-down and seconds dials, the latter with cut-away sector for access to the electrical contacts assembly, chrome satin finish to plates and balance cock, Earnshaw escapement, Mercer flatstrip detent to side of banking block, cut bi-metallic balance, circular heat compensation weights, palladium helical balance spring, winding through the dial, 'reverse' tipsy winding key and separate key for 'start/stop' control, the whole within an aluminium drum case with cap, contained in lidded black ebonite sorbo-rubber lined outer carrying box having polished aluminium quarter-round edging