Ruler

A ruler is a tool used to measure length. It has markings called rules along its edge that help you find out how long something is. You can also call a ruler a rule, scale, line gauge, or metre/meter stick. Rulers are usually made stiff so they stay straight, and this straight edge can help you draw straight lines too.

Rulers are very important in subjects like geometry, geography, and mathematics. People have been using rulers to measure things since at least the year 2650 BC, which means they have been a helpful tool for a very long time. Whether you are measuring the length of a piece of paper or drawing a straight line, a ruler is a simple but useful tool.

Variants

Rulers come in many sizes and are made from different materials. Long ago, rulers were mostly made from wood, but now plastics are also used. For stronger rulers, like those used in workshops, metal is used. Some rulers even have a metal edge attached to wood to help when drawing straight lines.

Common rulers are about 12 inches (30 cm) long, which is just right for use on a desk. Shorter rulers are easy to carry in a pocket, while longer ones, like yardsticks and meter sticks, are used when more length is needed. In the past, very long measuring tools were used for big projects, but today, tools like the tape measure, the surveyor's wheel, and laser rangefinders are more common.

Use in geometry

Main article: Compass and straightedge

In geometry, we can draw straight lines between points using a straightedge, which is just a ruler without any markings on it. This tool also helps us make accurate graphs and tables.

A special way to build shapes called a ruler and compass construction uses both a ruler and a compass. With these tools, we can split an angle into two equal parts, but it is impossible to split an angle into three equal parts using only a compass and straightedge. However, if we are allowed to make two marks on the ruler, we can solve this problem using a method called a neusis construction.

History

In the history of measurement, many ways to measure distance used parts of the human body, like the cubit, hand, and foot. These units changed in size over time and place. In the late 18th century, the metric system began, and now most countries use it.

One of the oldest measuring tools ever found is a copper bar from around 2650 BC, discovered in the Sumerian city of Nippur in Iraq. Rulers made from ivory were used by the Indus Valley civilization before 1500 BC.

Later, Anton Ullrich created the folding ruler in 1851, and Frank Hunt made the flexible ruler in 1902.

Curved and flexible rulers

A special tool called a French curve helps draw smooth curves, like a ruler but curved. There are also flexible tools, called flat splines or flexible curves, that can bend to any shape you need. Long ago, workers like masons used a bendable lead tool for curved molding, known as a lesbian rule.

Philosophy

Ludwig Wittgenstein used rulers as an example in his work Philosophical Investigations. He talked about how the standard meter bar in Paris was used to decide if other rulers were exactly one meter long. But, he said there was no way to prove that the standard meter bar was really one meter. It was just accepted as one meter in our way of talking and thinking.

Main article: Ludwig Wittgenstein

Main article: Philosophical Investigations