The bottom number is your timepiece's unique serial number, while the top is the model reference, which is identical for each watch of the model type. What do the serial and model numbers mean? The two numbers on the back of your TAG Heuer watch have different purposes.

TAG Heuer S.A., founded Heuer AG (/ˌtæɡ ˈhɔɪ. ər/ TAG HOY-ər) is a Swiss luxury watchmaker.

In a nutshell, while the vast majority of TAG Heuer watches do not hold value in comparison to the big luxury brands like Rolex and Patek Philippe, its rare or vintage pieces do hold excellent resale value and fare better in terms of value.

It's popular to hate on them because they're popular (the two luxury brands most people can even name) and since they aren't bought by the most discerning of consumer, stuffy enthusiasts turn their nose up at them. Tag turned themselves into the “Nickleback” of watches with cheap watches posing as luxury offerings.