The split-seconds chronograph is one of the three most difficult complications to master, alongside the tourbillon and the minute repeater. It takes a highly sophisticated mechanism to control the two chronograph hands, one of which may be stopped to measure an intermediate or lap time or retain a reference time while the other continues its course unaffected, even by fractions of a second. When released again, the split-seconds hand instantly catches up with the primary hand and the two stacked hands move on together.