Also known as 'remontoire escapement', and having many differing designs. These escapements achieve a uniform impulse by the use of the driving force to wind an auxiliary spring or weight during a detached part of the escapement's action; the energy stored in the auxiliary spring or weight is used to give impulse to the balance or pendulum while the clock train is locked, thereby providing a constant driving force to the escapement. The Secticon clock constant-force escapement was introduced in the 1960s. The driving motor roller winds the remontoire spring via the intermediate roller and the impulse arm, which is latched by the permanent magnet. On the anticlockwise vibration of balance, the impulse pin enters the fork of the impulse arm, which unlatches from the permanent magnet and gives impulse to the balance. At the end of the impulse arm's travel, the roller locking nib is advanced by pallet, enabling the action to continue. Constant-force escapements can give the highest performance, but cost of manufacture and difficulty in adjustment make this complicated escapement rather rare.