What truly makes a watch a “classic” watch? The truth of the matter is that in today’s world, determining whether a watch is “classic” or “dressy” is now partly subjective (thanks in part to a certain British super spy). Even with that said, here are some general rules of thumb.
Case: In short, the smaller the better, in both width and thickness. Keep in mind that most of the time you’ll be wearing a dress watch with a button down shirt, and that the watch should be thin enough to tuck under the shirt comfortably. Nowadays, one could say that the average size for a men’s watch is around 42mm. While any size lower than this should work well, keep in mind that the ideal size of a "classic" watch really depends on the wrist size of the wearer.
Design: Historically, “dressy” watches have looked incredibly simple, and sometimes almost sterile (you know, like a simple three-hander). This idea provides a great basis of understanding: in general, a “classic” watch should be handsome and understated. The Contemporary Classic (above, bottom) and Symphony (above, left) collection are great example of watches that are elegant, but not overly ornate to the point that they’ll take away from the rest of your outfit.
Strap: It goes without saying that simple leather or stainless steel straps are ideal for a dress watch, especially for formal events. It’s probably best that you leave your two-toned NATO straps at home.
Features: Many will say that the limit for watch features (or complications) should be maxed at one or two. This isn’t always the case, but limiting the complications on a watch ensures that the dial of the watch is uncluttered and distinguished.
Movement: There are definitely those that will argue that a mechanical movement is not necessary for a dress watch. And you know what, they’re perfectly right. But judging by the craftsmanship and skill it takes to create and manufacture such a movement, it seems natural that a classic watch should exude some kind of prestige and aura, and showcase an art that’s been developed and refined for hundreds of years.