Dressing index is in the weather forecast. How is this worked out?

Dressing index refers to the thickness of clothes needed to keep the body surface temperature constant or keep the human body comfortable. Wearing clothes is different from wearing a hat, but how to wear clothes makes you feel more comfortable? According to the weather conditions, such as sky conditions, temperature, humidity, wind, etc., which have the greatest influence on human body's perceived temperature, the Meteorological Bureau summarizes the weather index of dressing, which can remind you to dress in time according to weather changes and reduce the occurrence of colds.

Dressing index has eight grades.

1 grade heat, grade 2 heat, grade 3 slight heat, grade 4 cool, grade 5 cool, grade 6 slight cold, grade 7 cool and grade 8 cool.