Some history of the chronograph and it's importance in space.
History of the Chronograph
The chronograph literally translated means “Time Writer” — a union of the Greek word “chronos” meaning time and “graph” meaning writing. While this often confuses people as to why it would have the word “writing” in it, the very first versions of the chronograph were operated by marking the dial with a small pen that was attached to the index, whereby the length of the pen mark indicated how much time had elapsed. Invented in 1815, Louis Moinet created what would become the first chronograph upon its completion in 1816.
Moinet invented the chronograph solely as a tool for working with astronomical equipment. However, despite this creative invention, it was a man named Nicolas Mathieu Rieussec who built the first chronograph to actually be offered in the marketplace. Commissioned by King Louis XVIII in 1821, Rieussec was a French watchmaker who gained respect from the King for being publicly known as not being a loyal follower of Napoleon.
(More stuff I didn’t pick up from the story here)
After the Wright Brother’s success introduced aviation to a world fascinated with flight, the demand for chronographs rose considerably. Just as a chronograph is useful in aviation, it stands to reason that other industries requiring very precise or repeated timing could benefit from such a mechanism.
No longer was the chronograph simply used for horse racing and aviation, it was now introduced to automobile racing, Olympic sport and of course, naval and submarine navigation. Due to the varying demands, the watch industry began to produce a variety of chronographs such as the Flyback, which allows the second hand to be rapidly reset; the Rattrapante, where multiple second hands can be stopped and started independently; and the minute and hour times, which were designed in various ways including water-proof models for deep sea diving and water sports.
President Eisenhower, a renowned watch collector and horologist, had ordered that with the evolution of space exploration by NASA, all test pilots and astronauts would be required to wear a chronograph on their wrist. On April 15, 1970, just 56 minutes after launching and 200,000 miles from Earth, an explosion occurred aboard Apollo 13 that crippled the shuttle and resulted in what NASA believed was going to be the certain death and loss of Apollo 13’s three astronauts and the capsule they were flying blind in. As the world watched and waited helplessly gripping the edge of their seats, two days later, on April 17, 1970, the astronauts returned safely to earth, thanks to the Omega Speedmasters they were equipped with due to President Eisenhower’s order. The astronauts were able to use the chronograph function to time a critical engine burn despite all onboard computers having failed. Able to recalculate their reentry to earth, they successfully aligned the capsule which resulted in a safe splashdown. When Americans realized that a simple wrist watch had saved the lives of these men when no technologically advanced super computer could; the entire world once again took notice, comparing the newly popular electronic watches to the technology that had failed onboard Apollo 13. Today, the vast majority of commercial, civilian and military pilots wear chronographs, on the off chance their systems fail and a simple mechanical watch is needed to save them and any other souls on board their aircraft.
How to use a Chronograph
https://www.youtube.com/watch?v=GPHpn4N9D6o
A double chronograph allows the measurement of intervals.
Top dial tracks seconds
Bottom dial tracks number of times the top has gone around.
So looking at this watch, it suggests 30 minutes elapsed at the time shown on the reset. Is the 30 countdown referenced with the date of 19 shown?
Or, that at 4:49 or 4:50 whichever you want to argue is shown on the watch face showing 19, that the action actually began at 4:20.