A hairspring, also known as a balance spring, is a crucial component in the timekeeping mechanism of a mechanical watch. It is a delicate, coiled spring that works in conjunction with the balance wheel to regulate the movement of the watch. The hairspring is responsible for controlling the oscillations of the balance wheel, ensuring that it moves at a consistent rate. This consistency is vital for maintaining accurate timekeeping. The hairspring's design allows it to expand and contract with each oscillation, propelling the balance wheel and enabling the watch to "tick." Typically made from materials like iron-nickel alloys, such as Nivarox, the hairspring is engineered to be resistant to temperature variations, which helps maintain its elasticity and performance. The invention of the hairspring in 1675 by Christian Huygens marked a significant advancement in watchmaking, as it allowed for more precise timekeeping. The combination of the balance wheel and hairspring is often referred to as the "regulating organ" of the watch, highlighting its essential role in the watch's functionality.