What is the little hole at the end of your ruler really for? It’s not for drawing circles!

What is the little hole at the end of your

If you look closely at your ruler, you will probably find a small rounded hole in it. We explain its real usefulness to you.

In mathematics you need to have good equipment: ruler, compass, square… The ruler is also an essential part of the perfect schoolchild’s kit because it is used almost every day. 20cm, 30cm, rigid, flexible, there are many models. They can be used to draw straight lines, underline or measure a distance. Even on a daily basis, it can be useful to have one at home. That being said, some have a little particularity. It has a small hole at the end. What can it possibly be used for?

If you thought the goal was to be able to draw little circles, that’s not the case. Many students also have fun with this hole by putting their pen in it to turn the ruler but obviously, that is not why it was created. If today this little hole no longer seems to have any real use, it was not there for nothing. We must, in fact, go back into the history of this tool to understand.


The oldest measuring rod was discovered in 1500 BC in the Indus Valley at Lothal (present-day western India) and was made of ivory. During Antiquity, the rule became popular with the standardization of units of measurement. Furthermore, the first rules were not necessarily graduated and therefore lacked precision. In the Middle Ages, the unit of measurement developed with the “inch”. It was only in 1791, after the French Revolution, that the meter saw the light of day and the rulers were then graduated in centimeters. The rule was then used more and more in schools.

It was in the 19th century that the small hole appeared on school rules. Schoolchildren writing on slates could, using a string passed through this small hole, attach their ruler to their slate. Chalk and cloth were also often linked with the rest to have everything within reach.

Since the slates have now disappeared, the hole in the ruler has lost its original usefulness. However, you can still use this hole to attach your ruler if you don’t want to lose it. For example, with a small nail you can hang your ruler on one side of your desk. This can also allow, if you are taking measurements, to hold the ruler securely by putting a pin or the tip of a pen in the small hole.