Chronographs Back to Which Watch?
Chronographs
are timepieces that can measure time simultaneously. Besides normal timekeeping
they can be used for multiple specific measurements of time. The measurements
are read from sub dials within the main dial. A central second hand can be
started and stopped, without interfering with the continuous time.
Many chronographs also have a tachometer scale. This allows the user to measure speed traveled over a given distance. For instance you can judge the speed of a racing car by initiating the timer as the car passes over the start of the given distance point measuring 1000m. The timer is stopped after the second point is reached. The chronograph hand will end up pointing to a figure on the tachograph scale which is the speed of the car. Typically this function is used in motor sport, cycling and avionics - both civil and military.
Some chronographs have a telemeter scale as well. This allows you to measure the speed of sound in relation to the speed of light. For example, to judge how far away a storm is, you activate the counter when you see the lightning flash. You stop the counter when you hear the thunder. The indication on the telemeter scale that the chronograph hand is pointing to is the distance in kilometers. This may sound like a futile function but has invaluable practicalities in military applications where artillery forces can judge the distance of bombs that they are firing - or that are being fired at them!
One of the most famous chronographs is perhaps the Omega Speedmaster, which has long been used by NASA astronauts during manned space flights. This watch operates flawlessly in space, which the most extreme environment known to man. As well as it being zero gravity, there are temperature fluctuations from as hot as +120C to as low as -156C. This temperature change can be instantaneous as an astronaut moves from shade to direct sunlight. The most remarkable fact about the Speedmaster is that it is a standard watch that was being sold for everyday use that NASA astronauts use. Omega did not need to make any special changes to the design when NASA began its rigorous testing.
Most
famously, it was the Speedmaster's accurate timing that enabled the astronauts
aboard the Apollo 13 ill fated mission, to return safely back to Earth.