.....What does the outer rim "1 mile" etc refer to?
That's the telemeter scale and is used to measure the distance of an event that is both visible and audible.
For example, on a Military chrono, typically you start the timer at the sight of a distant flash of gunfire, stop it when you hear the sound, and then read off the distance of the flash on the scale.
(Then you take a bearing and whistle up a concentrated hate on the bastard shooting at you)You can also use it to estimate the distance of a thunderstorm.
The markings and scales do vary depending on who or what the chrono is designed for ie Military, Aviators, Doctors, Engineers, Sportsmen, Divers or even Astronauts.
Sometimes there will be an additional rotating outer bezel too with markings that can be used with the inner fixed dial marking scales as a rotary slide rule calculator.