Which mechanical feature allows certain moon phase watches to display crescent shapes?

The disc mechanism is the feature that allows certain moon phase watches to display crescent shapes. This mechanism typically involves a rotating disc that is marked with different phases of the moon. As the disc advances, it reveals the crescent shapes as seen from Earth, indicating the moon's current phase, such as new moon, first quarter, full moon, and so on.

The design ensures that as the disc rotates, the portion of the moon visible through an aperture on the watch dial changes shape, effectively replicating the lunar cycle in real-time. This visual representation not only adds aesthetic value but also serves a functional purpose for users interested in lunar phases for various reasons, from gardening to fishing.

The other mechanical features, while important in watch design, do not specifically enable the crescent shape display of moon phases.