No one can draw a straight line unassisted, not unless you’re one of those extremely rare geniuses. Even professional artists and designers don’t leave straight lines up to chance or fate, utilizing a tool to ensure those marks keep in line. The most common tool for this kind of drawing is, of course, the ruler, and it doesn’t get any simpler than a piece of wood, metal, or plastic with a straight edge. Not unless you count this odd-looking metal piece with a small cog-like wheel, a contraption that could very well be the simplest way to draw a straight line, one that doesn’t obscure any part of the page or risk accumulating ink and dirt that would later smudge on your work.

Designer: Gihawoo Design (UGLY.DUCKLING)

When you simply want to draw a straight line, technically, any object that you can run your pen or pencil along its straight edge will do. If you need to draw a straight line with a specific length, then you’ll need something that has markings for units of length, which is precisely what a ruler brings to the table, pun intended. But while the venerable ruler’s design is simple and effective, it also comes with flaws that most people simply overlook.

For one, a ruler almost always covers up a chunk of what’s already on the page, though there are also transparent rulers that try to remedy that situation. Running an ink pen along the edge of the ruler also transfers some of that ink to that edge, ink that could smudge on the page when you lift or move the ruler. There are a few rulers that have raised edges for that very purpose, but these are far and few in between.

The Constrained Ball represents a solution that tackles the problem from a completely different angle. There’s nothing that says you actually need a long object to draw a straight line, only that there needs something to guide the pen on that path. This object does exactly that by using a wheel that rolls along a straight line, dragging an inserted pen in tow. Any pen size will do, given how the rubber hole can stretch to accommodate a larger barrel. There’s also an option to have a small LCD display that measures the distance traveled by the wheel based on its rotations to accurately measure the length of the line.

It is admittedly a simple and creative alternative to a ruler, one that reduces the risks of smudging and doesn’t cover up any content on the page. There might be some concerns about how straight your hand can really travel with this guide, or more importantly, you can actually draw parallel lines without being able to “see” the line beforehand, like with a ruler. Still, for most use cases, this rather cute little thingamajig will do, and it will more easily fit in your pouch or tool case better than any foot-long ruler.