Functions like this or the display of a second-time zone are referred to as minor complications, also justified concerning complications such as the minute repeater or the perpetual calendar. But it is precisely the so-called minor complications that are of practical importance.
The technical implementation of the window date is more difficult to realize than the pointer date. Both are based on the exact minute drive in the middle of the movement. The change in the date is based on a component with a small diameter, the direction of which has to be transferred to the date display on the edge of the movement, i.e., to a much larger diameter. Here, angle errors and difficulties in jumping the date must be overcome. And finally, the window display shows a higher energy loss than the pointer version due to the higher friction and the additional weight of the date disc.
The Big Date
The watch Rolex oyster perpetual with the outsize date is and will remain unbeaten when it comes to readability. This function was particularly influential at the Saxon manufacturer A. Lange & Söhne: especially the legendary Lange 1. Many other models would certainly not have become as famous as today without the two windows. The single disc and the tens cross of Lange’s date display are at a minimal height difference from one another. To hide this, the outsize date appears in a window with a rung.
So, the outsize date is an excellent and functional solution. Not only does it make it easier to read, but it is also a design feature in its own right, as well as a notable technical complication.