Balance Spring - Regulator

In order to adjust the rate, the balance spring usually has a regulator, a moveable lever with a narrow slit on the end through which the last turn of the spring passes. The portion of the spring after the slit is held stationary, so the slit controls the usable length of the spring. Moving the regulator slides the slit up or down the spring, changing its effective length. Moving it away from the spring's attachment point (stud) shortens the spring, making it stiffer, increasing the balance's oscillation rate, and making the timepiece gain time.

In older watches, the slit is the gap between two tiny pins, called the Curb Pins.

The regulator interferes slightly with the motion of the spring, causing inaccuracy, so precision timepieces like marine chronometers and some high end watches are free sprung, meaning they don't have a regulator. Instead, their rate is adjusted by timing screws on the balance wheel.

There are two principal types of Balance Spring Regulator.

• The Tompion Regulator, in which the Curb Pins are mounted on a sector-rack, moved by a pinion. The pinion is usually fitted with a graduated silver or steel disc.
• The Bosley Regulator, as described above, in which the Pins are mounted on a lever pivoted coaxially with the Balance, the extremity of the lever being able to be moved over a graduated scale. There are several variants which improve the accuracy with which lever can be moved, including the "Snail" regulator, in which the lever is sprung against a cam of spiral profile which can be turned, the Micrometer, in which the lever is moved by a worm gear, and the "Swans Neck" or "Reed" regulator in which the position of the lever is adjusted by a fine screw, the lever being held in contact with the screw by a spring in the shape of a curved swans neck. This was invented and patented by the American George P. Reed, US patent No. 61,867 dated February 5, 1867.

There is also a "Hog's Hair" or "Pig's Bristle" regulator, in which stiff fibres are positioned at the extremities of the Balance's arc, and bring it to a gentle halt before throwing it back. The Watch is accelerated by shortening the arc. This is not a Balance Spring Regulator, being used in the earliest Watches before the Balance Spring was invented.

There is also a Barrow Regulator, but this is really the earlier of the two principal methods of giving the Mainspring "set-up tension"; that required to keep the Fusee chain in tension but not enough to actually drive the Watch. Verge Watches can be regulated by adjusting the set-up tension, but if any of the previously described Regulators is present then this is not usually done.