In the world of floating mainsail tacks, when you pull on the cunningham, a horizontal wrinkle often develops along the foot because the cunningham grommet moves down but the tack stays in place. Wouldn’t it be nice if both moved as one unit? This would allow for maximum projected sail area and a smoother shape. It can, and it’s easy.
From your standard cunningham purchase, attach a pennant of Dyneema to go up through the cunningham grommet, down through a small block or low friction ring tied off at or near the gooseneck, and then back to a grommet in the tack. I generally stick a small “dog bone” in the end of the pennant for easy rigging and de-rigging.
Now, when you pull cunningham, the tack will bottom out, and the cunningham will continues to work as it did before. As an added benefit, the system doesn’t technically add purchase, so it is legal in many one-designs, but be sure to check your class rules anyway.