Where to find reference number?
The majority of premium brands mark the product with the collection name on the dial and the reference number on the backside (rarely - on the case).
Searching by the reference number
Find the reference number (a combination of numbers and letters) in the accompanying documents. It gives all of the needed information: the type of the mechanism, the diameter of the case, the arrangement of the dial, the material of the case/strap.
Searching by the serial number
A serial number (engraved numbers on the backside) tells about the authenticity of the item and the year of production.