to approximately measure the distance to an event that can be both seen and heard (e.g. a lightning bolt or a torpedo strike) using the speed of sound. The user starts the chronograph (stopwatch) at the instant the event is seen, and stops timing at the instant the event is heard. The seconds hand will point to the distance measured on a scale, usually around the edge of the face. The scale can be defined in any unit of distance, but miles or kilometers are most practical and commonplace. See also Gun chronograph Marine chronometer Poljot Strela References External links Chronograph watches Keulen, Robert. 1996. Accessed 25 MAR 2012 Patek Philippe Chronograph Comparison Gray & Sons NOV 2014 A technical perspective, the chronograph, Monochrome-watches, Xavier Markl, February 2016 TAG Heuer’s 01 chronograph watch movement explained with videos WatchTime June 2016 Cronosurf - The online chronograph Measuring instruments Watches Timers