Sunny Saturday, oldie but goodie 1958 Big Seahorse cal 501 time. Still in love after all these years.
I believe the first image is the correct placement of a Mile telemeter bezel Sound travels through air at "the speed of sound." Officially, the speed of sound is 331.3 meters per second (1,087 feet per second) in dry air at 0 degrees Celsius (32 degrees Fahrenheit). At a temperature like 28 degrees C (82 degrees F), the speed is 346 meters per second. As you can see, the speed of sound changes depending on the temperature and the humidity; but if you want a round number, then something like 350 meters per second and 1,200 feet per second are reasonable numbers to use. So sound travels 1 kilometer in roughly 3 seconds and 1 mile in roughly 5 seconds. How Stuff Works