It is a tachymeter. (Once you know that, the big yellow T makes sense.) This a common enough thing on luxury watches - I didn't actually know this, but this morning I saw a glossy ad for one on the back of a magazine and recognized the scale. If you search tachymeter on Amazon or the like you can see any number of images.
The purpose of it is to determine speed. Going a certain distance in a given time means you are going a particular speed. You would need to learn what units your watch ring is in (km/hr or mph for example) and what the calibration distance is, but then you could say that going that far in about 10 seconds means you're going 30 somethings, or going that far in 20 seconds means you're going 15 somethings.
More expensive watches run the scale to a higher number, presumably because people who buy that kind of watch are in faster cars, jets etc but this only means a longer calibration distance, no change in the capabilities of the watch.