Draw a ball on several sheets of paper and flip through them. If the sheets slip sideways, the ball appears to jump even when you intended it to stay still. Traditional animation solves this basic alignment problem with registration: each drawing returns to a consistent position.
The quiet job of the peg bar
A peg bar fits corresponding holes in animation paper. The artist can exchange sheets while keeping their reference position. Toon Boom’s explanation of pegs connects this physical practice with the digital tools that inherited its name. Hole arrangements vary between systems, so paper and bar must match.
The bar does not make the drawings identical. It gives the differences between them a stable background. A deliberately moving hand should move because its drawn position changes, rather than because the entire sheet has shifted.
Try a small registration exercise
Use a compatible bar and a few sheets of punched paper. Draw a stationary reference shape on each sheet, then add a second shape that changes position. Flip the sheets while they remain registered. The stationary shape gives your eye a simple check: if it wanders, inspect the alignment before deciding that the moving shape needs redrawing.
Keep the exercise short. A handful of drawings is enough to reveal the difference between intended motion and movement of the page. Do not judge the timing from a single still image; the effect belongs to the sequence.
Registration continues at the scanner
Scanning can introduce another alignment step. Toon Boom’s scanning documentation discusses handling the peg-hole area for registration. Follow the instructions for the actual scanner and software rather than assuming that placing every page roughly straight is sufficient.
In digital animation, a peg can instead be a control that moves or groups artwork. That does not mean a physical bar is hidden inside the application. The shared idea is a dependable relationship between elements. Once that relationship is stable, an animator can choose the movement instead of fighting accidental drift.