The role of chest protector

What is the leather that archers wrap around their left shoulder and left chest called? What is its function?

This smooth fabric is used to reduce friction when helping archers judge whether the bow is standard. When shooting arrows, if the action is the same as the last time, the arrow will hit the target very centrally. Everyone's actions are different, and the key is whether the two times can be guaranteed to be the same. One of the actions is bowing. Bowing is usually judged by the nose, lips, and jaw. If the bow action is the same as the last time, then the bow should be at a fixed point in these three parts each time.

That's why some archers always have a groove on their chins (from thousands of bows). The chest can also be used as a reference for bowing, because when the action is standard, the string will definitely be on the chest. The existence of this fabric is to prevent the string from leaning on the clothes. The wrinkles on the clothes will produce unpredictable resistance to the string at the moment of release, causing instability at the moment of arrow shooting.