A balance spring, or hairspring, is a part used in mechanical timepieces. The balance spring, attached to the balance wheel, controls the speed at which the wheels of the timepiece turn, and thus the rate of movement of the hands. A regulator lever on the balance spring is used to adjust the speed so that the timepiece keeps accurate time.

The balance spring is a fine spiral or helical torsion spring used in mechanical watches, marine chronometers, and other timekeeping mechanisms to control the rate of oscillation of the balance wheel. A balance spring usually has a regulator lever to adjust the rate of the timepiece, but other designs use adjusting screws on the balance wheel instead. The balance spring is an integral part of the balance wheel, because it reverses the direction of the balance wheel causing it to oscillate back and forth. The balance spring and balance wheel together form a harmonic oscillator, whose resonant period is resistant to changes from perturbing forces, which is what makes it a good timekeeping device.

Heidi Samuel Klum (born June 1, 1973), better known by her birth name Heidi Klum, is a German and American model, actress, television host, businesswoman, fashion designer, television producer, and occasional singer. In 2008 she became an American citizen while maintaining her native German citizenship. In January 2012, Klum separated from her husband, British musician Seal and filed for divorce on April 6, 2012.

Klum was born and raised in Bergisch Gladbach, a town outside Cologne. She is the daughter of Erna, a hairdresser, and Günther Klum, a cosmetics-company executive. A friend convinced her to enroll in a national modeling contest called "Model 92". Out of 25,000 contestants, Klum was voted the winner on April 29, 1992 and offered a modeling contract worth US$300,000 by Thomas Zeumer, CEO of Metropolitan Models New York. After winning, she appeared on the Gottschalk Late Night Show, a top German television show with host Thomas Gottschalk. She accepted the contract a few months later after graduating from school and decided not to try for an apprentice position at a fashion design school.