English: Watchmaker's hairspring "vibrating" tool, from Switzerland 1910. This was used by watchmakers to adjust the length of a balance wheel's hairspring before installing it in a watch. The hairspring was attached to the tiny pointed clamp, and the balance wheel was suspended from the vertical arm, hanging by its hairspring. The balance was set rotating back and forth, and its period was compared with the period of the precision calibrated balance wheel mounted under the glass in the base. The clamp was moved up and down the hairspring until the two balance wheels rotated in synchronism. This determined the proper point on the hairspring for the lever curb pins.