Why do they install a ruler at the entrance to stores in the US (5 photos)
Many who have visited the United States have been surprised to notice a vertical ruler at the entrance to American stores. It can be attached to the left of the entrance or even in the middle of sliding doors.
There are many theories about the purpose of this thing, but few people outside of American retail workers know the correct answer. 
There are many possible uses for the ruler. Some will assure you it's designed for tall people to prevent them from hitting their heads, while others will say it helps estimate the dimensions of large items being carried out the door. There are even stranger explanations, born of the boundless human imagination. 
In fact, the height scale near the door of a store is a crime-fighting measure introduced back in the 1970s. Shoplifters back then weren't particularly courteous to those who tried to object, immediately resorting to weapons.
Therefore, authorities trained citizens to be, first and foremost, good witnesses, not heroes. Salespeople and customers at supermarkets, jewelry stores, and cafes were strongly advised not to resist robbers, but to watch them closely. 
"Treat them like your best customer: give them what they want and show them the door," was the basic rule of conduct in the event of a robbery. A ruler at the entrance allows for the most accurate recording of an important characteristic of the attacker that cannot be changed—their height. 
A person under stress tends to exaggerate the height of a robber. That's why police often looked for two-meter-tall men, instead of skinny, short bandits.
The ruler effectively solves this problem, eliminating human error. Even if everyone present during a robbery panics and forgets to look at the ruler, the height of the robbers will be recorded by surveillance cameras aimed at the entrance.
Not only retail workers know about rulers, but criminals too. Statistics show that stores equipped with such a device are attacked much less frequently. Therefore, this innovation, recommended by the police, has already become popular. 
7-Eleven was the first retailer to introduce mandatory height measuring rulers in all its stores.
Over the course of 10 years, from 1976 to 1986, the number of late-night robberies at the chain's convenience stores decreased by 50 percent. Based on this experience, the National Association of Convenience Stores recommended the use of the rulers, and they were installed in thousands of stores across the United States.
