The flying saucer- / disco-volante-called case-shape has the lugs not externally attached to the case but includes them somehow into the case. This is just on one side a design-element to make a watch look beautiful. On the other side it is one of the most effective ways to reduce the optical size of a watch and to make even large and over-sized watches wearable for an average wrist-size.

This was especially useful when the movements were requiring case-sizes that appear gigantic in that respective era: the first Swiss quartz-movements like the Beta21 (1970, top-row & middle-right), the Longines Ultra-Quartz (1969, middle-left), the Girard Perregaux cal350 (1972, bottom-left) and the Omega cal1500 (bottom-right) for example. The design-hack to include the lugs made these significant and over-sized watches wearable icons.