The principle behind shuttlecock speed:

The speed of a badminton shuttlecock is determined by its weight. The heavier the shuttlecock, the faster it flies. The numbers 76, 77, and 78 on the tube represent the weight unit "grain." Therefore, a shuttlecock with a speed of 78 is heavier and flies faster than a shuttlecock with a speed of 76.

76 Speed (Quite Slow): 25-30℃. Suitable for Southern European summers (e.g., Spain, Southern Italy) and Southern North American summers.

77 Speed (Average/Medium): 15-25℃. Suitable for British spring and autumn, Northern European summers, and North American standard-temperature stadiums.

78 Speed (Quite Fast): 0-15℃. Most commonly used year-round in the UK, Northern European autumn and winter, and Northern North American winters. Most popular in Europe and America.